BIO - TERMS - ENZYME Flashcards
2ʹ-O-methyltransferase (MTase)
An enzyme that transfers a methyl group to the 2ʹ hydroxyl of the first and second ribose groups in mRNA. Viruses that acquire MTase can produce cap-1 and cap-2 on their transcripts and thereby evade restriction by IFIT1.
21-hydroxylase
An enzyme of non-immune function but encoded in the MHC locus required for normal cortisol synthesis by the adrenal gland.
7α-Hydroxylase
The regulated enzyme of bile acid synthesis.
acetyl CoA
Small water-soluble activated carrier molecule. Consists of an acetyl group linked to coenzyme A (CoA) by an easily hydrolyzable thioester bond.
Acetylcholinesterase
An extracellular acetylcholinedegrading enzyme in cholinergic synapses.
acid hydrolases
Hydrolytic enzymes—including proteases, nucleases, glycosidases, lipases, phospholipases, phosphatases, and sulfatases—that work best at acidic pH; these enzymes are found within the lysosome.
acrosome
(ak′rō-sōm) A cap-like structure on the anterior two-thirds of the sperm nucleus that contains digestive enzymes for penetrating an oocyte.
ADA–SCID (adenosine deaminase-defi cient severe combined immunodefi ciency disease)
An autosomal recessive disorder in humans caused by a lack of the enzyme adenosine deaminase, which catalyzes the breakdown of deoxyadenosine. In the absence of this enzyme, toxic derivatives of this nucleoside accumulate and kill cells required for normal immune responses to infections.
Adenylate cyclase
The cyclic adenosine monophosphate (cAMP)-synthesizing enzyme, located in the plasma membrane.
Alanine transaminase (ALT)
A liver enzyme; its serum level is elevated in liver diseases.
Alcohol dehydrogenase
A cytosolic liver enzyme that oxidizes ethanol to acetaldehyde.
alcohol fermentation
A catabolic process, beginning with glycolysis, that produces ethyl alcohol to reoxidize NADH.
Alkaline phosphatase
A diagnostically useful enzyme in bones and the biliary system.
allosteric enzyme
A regulatory enzyme with catalytic activity modulated by the noncovalent binding of a specific metabolite at a site other than the active site.
allosteric inhibition
The process in which an enzyme’s activity is changed because of binding to the allosteric site.
Allozyme
A variant of an enzyme detected by electrophoresis.
amine oxidase
Copper-containing enzyme that catabolizes certain amino acids, such as histidine and tyramine. amino acid A compound that contains a central carbon that has an amine group, a carboxyl group, and a hydrogen atom and has a side chain (R) bonded to it. It is the building block of proteins.
Aminolevulinic acid (ALA) synthase
The regulated enzyme of heme biosynthesis.
aminotransferases
Enzymes that catalyze the transfer of amino groups from α-amino to α-keto acids; also called transaminases.
antibody-directed enzyme/pro-drug therapy (ADEPT)
Treatment in which an antibody is linked to an enzyme that metabolizes a nontoxic prodrug to the active cytotoxic drug.
antimicrobial enzymes
Enzymes that kill microorganisms by their actions. An example is lysozyme, which digests bacterial cell walls.
APOBEC1 (apolipoprotein B mRNA editing catalytic polypeptide
1) An RNA editing enzyme that deaminates cytidine to uracil in certain mRNAs, such as apolipoprotein B, and which is related to the enzyme AID involved in somatic hypermutation and isotype switching.
Arginase
The urea-forming enzyme of the urea cycle.
Aromatase
The enzyme that converts androgens to estrogens.
ATPase
An enzyme that hydrolyzes ATP to yield ADP and phosphate, usually coupled to a process requiring energy.
autolysis
(aw-tol′i-sis) Digestion of cells by enzymes present within the cell itself.
beer
Alcoholic beverage produced by fermentation of starch.
binding energy
The energy derived from noncovalent interactions between enzyme and substrate or receptor and ligand.
bioluminescence
The emission of light from the electron transport chain; requires the enzyme luciferase.
bioreactor
A fermentation vessel with controls for environmental conditions, e.g., temperature and pH.
blob
A collection of cells, mainly in primary visual cortical layers II and III, characterized by a high level of the enzyme cytochrome oxidase.
Brush border enzymes
Enzymes on the luminal surface of intestinal mucosal cells.
C3 convertase
Enzyme complex that cleaves C3 to C3b and C3a on the surface of a pathogen. The C3 convertase of the classical and lectin pathways is formed from membrane-bound C4b complexed with the protease C2a. The alternative pathway C3 convertase is formed from membrane-bound C3b complexed with the protease Bb.
C3b2Bb
The C5 convertase of the alternative pathway of complement activation.
C3bBb
The C3 convertase of the alternative pathway of complement activation.
C4b2a
C3 convertase of the classical and lectin pathways of complement activation.
C4b2a3b
C5 convertase of the classical and lectin pathways of complement activation.
C5 convertase
Enzyme complex that cleaves C5 to C5a and C5b.
Catalytic rate constant
The rate constant kcat that describes the rate of product formation from the enzyme-substrate complex.
Catechol-O-methyltransferase (COMT)
A catecholamine-inactivating enzyme.
cGAS (cyclic GAMP synthase)
A cytosolic enzyme that is activated by double-stranded DNA to form cyclic guanosine monophosphate-adenosine monophoshate. See cyclic dinucleotides (CDNs).
Chalcone synthase
Key enzyme for the biosynthesis of polyketides like flavonoids and anthocyanins.
channeling
The direct transfer of a reaction product (common intermediate) from the active site of an enzyme to the active site of the enzyme catalyzing the next step in a pathway.
Choline-acetyltransferase
The acetylcholine-synthesizing enzyme in nerve terminals.
Cholinesterase
A serum enzyme that participates in the metabolism of some drugs.
coagulase
A bacterial enzyme that causes blood plasma to clot.
coenzyme B12
An enzymatic cofactor derived from the vitamin cobalamin, involved in certain types of carbon skeletal rearrangements.
collagenase
An enzyme that hydrolyzes collagen.
competitive inhibitor
A chemical that competes with the normal substrate for the active site of an enzyme. See also noncompetitive inhibitor.
Covalent catalysis
A catalytic mechanism that involves the formation of a covalent bond between enzyme and substrate.
Creatine kinase
An enzyme whose level is elevated in the serum of patients with muscle diseases and acute myocardial infarction.
creatine phosphokinase
(CPK)—An enzyme contained in the phosphagen system that adds a phosphate to taken from phosphocreatine to and adenosine diphosphate to create ATP.
cyclic AMP phosphodiesterase
Specific enzyme that rapidly and continuously destroys cyclic AMP, forming 5′-AMP.
cyclic AMP-dependent protein kinase (protein kinase A, PKA)
Enzyme that phosphorylates target proteins in response to a rise in intracellular cyclic AMP.
cyclic GMP phosphodiesterase
Specific enzyme that rapidly hydrolyzes and degrades cyclic GMP.
cytochrome c oxidase
A copper-containing multisubunit polypeptide enzyme complex in the electron transport chain that is involved in the production of ATP and water.
Cytochrome P450 monooxygenase
Very large superfamily of enzymes containing a heme-iron center present in all organisms and involved in the oxidation of compounds. Cytochrome P450s are one of the driving factors in metabolic diversity.
cytoplasmic tyrosine kinase
Enzyme activated by certain cell-surface receptors (tyrosine-kinase-associated receptors) that transmits the receptor signal onward by phosphorylating target cytoplasmic proteins on tyrosine side chains.
dehydrogenases
Enzymes that catalyze the removal of pairs of hydrogen atoms from substrates.
Deoxyribonuclease (DNase)
Any enzyme that hydrolyzes DNA.
Dihydrofolate reductase
An enzyme that reduces dihydrofolate to tetrahydrofolate.
Dioxygenases
Enzymes that incorporate both oxygen atoms of O2 in their substrate.
Direct-acting antivirals
Drugs that inhibit viral enzymes. (Chapter 9) Disseminated infection An infection that spreads beyond the primary site; oft en includes viremia and infection of major organs such as the liver, lungs, and kidneys. (Chapter 2)
dissimilation plasmid
A plasmid containing genes encoding production of enzymes that trigger the catabolism of certain unusual sugars and hydrocarbons.
DNA glycosylases
Enzymes that remove abnormal bases from DNA.
DNA gyrase
An enzyme in bacteria that catalyzes the formation of negative supercoils in DNA.
DNA ligase IV
Enzyme responsible for joining the DNA ends to produce the coding joint during V(D)J recombination.
DNA photolyase
An enzyme that uses energy from blue light to cleave ultraviolet light-induced covalent cross-linkages in thymine, cytosine, and cytosine-thymine dimers in DNA.
DNA repair enzymes
Enzymes that catalyze the repair of damaged DNA.
dopamine hydroxylase
A copper-containing enzyme that converts dopamine to norepinephrine.
E3 ligase
An enzymatic activity that directs the transfer of a ubiquitin molecule from an E2 ubiquitin-conjugating enzyme onto a specific protein target.
ELISA (enzyme-linked immunosorbent assay)
A group of serological tests that use enzyme reactions as indicators.
endoplasmic reticulum aminopeptidase associated with antigen processing (ERAAP)
Enzyme in the endoplasmic reticulum that trims polypeptides to a size at which they can bind to MHC class I molecules.
endoplasmic reticulum-associated protein degradation (ERAD)
A system of enzymes in the endoplasmic reticulum that recognizes incompletely or misfolded proteins and assures their eventual degradation.
Enteropeptidase
An enzyme that activates trypsinogen in the duodenum.
enzyme cascade
A series of reactions, often involved in regulatory events, in which one enzyme activates another (often by phosphorylation), which activates a third, and so on. The effect of a catalyst activating a catalyst is a large amplification of the signal that initiated the cascade.
enzyme-coupled receptor
A major type of cell-surface receptor that has a cytoplasmic domain that either has enzymatic activity or is associated with an intracellular enzyme. In either case, the enzymatic activity is stimulated by an extracellular ligand binding to the receptor.
epimerases
Enzymes that catalyze the reversible interconversion of two epimers.
extremozymes
Enzymes produced by extremophiles.
F(abʹ)2 fragment
Antibody fragment composed of two linked antigenbinding arms (Fab fragments) without the Fc regions, produced by cleavage of IgG with the enzyme pepsin.
fatty acid synthase
A complex of multiple enzymes involved in the synthesis of fatty acids.
ferroxidase
A copper-containing enzyme (e.g., ceruloplasmin) that has a profound effect on iron metabolism by promoting the conversion of the ferrous form of iron to the ferric form.
flavin nucleotides
Nucleotide coenzymes (FMN and FAD) containing riboflavin.
flavin-linked dehydrogenases
Dehydrogenases requiring one of the riboflavin coenzymes, FMN or FAD.
Fructokinase
The major fructose-metabolizing enzyme.
Fructose intolerance
Hereditary disorder caused by deficiency of a fructose-metabolizing enzyme.
Fructose-1,6-bisphosphatase
An important regulated enzyme of gluconeogenesis.
Galactokinase
The enzyme that phosphorylates galactose to galactose-1-phosphate.
Galactosemia
A hereditary disease caused by the deficiency of a galactose-metabolizing enzyme.
gene editing
A technique to add, delete, or insert DNA in a chromosome using bacterial enzymes.
Glucokinase
The liver isoenzyme of hexokinase.
Glucose-6-phosphatase
The glucose-producing enzyme in gluconeogenic tissues and glucose-transporting epithelia.
Glucose-6-phosphate dehydrogenase
The first enzyme in the oxidative branch of the pentose phosphate pathway.
Glucose-6-phosphate dehydrogenase deficiency
A common enzyme deficiency that leads to hemolysis after exposure to certain drugs.
Glucosinolates
Nitrogen and sulfur containing Sglycosides derived from aliphatic and aromatic amino acids. The enzyme myrosinase cleaves this glycosidic bond and releases (iso)thiocyanides or nitriles as potent defense compounds.
Glutamate dehydrogenase
An enzyme that catalyzes the oxidative deamination of glutamate and the reductive amination of α-ketoglutarate.
Glutaminase
A hydrolytic enzyme that releases ammonia from glutamine.
glutaric aciduria type 1
An inborn error of tryptophan metabolism resulting from a defect in the enzyme glutaryl CoA dehydrogensase, which is involved in the breakdown of tryptophan. An intermediate breakdown product, glutaryl CoA, is converted to glutaric acid, which accumulates in fluids. This accumulation of glutaric acid may lead to seizures, acidosis, and an enlarged head.
glutathione peroxidase
A selenium-containing antioxidant enzyme that functions to convert hydrogen peroxide (produced by the enzyme catalase) to water.
Glutathione reductase
An NADPH-dependent enzyme that keeps glutathione in the reduced state.
Glutathione-S-transferase (GST)
This enzyme catalyzes conjugation of the reduced form of glutathione to xenobiotic substrates for the purpose of detoxification. The enzyme is involved in the detoxification of reactive oxygen species.
Glycogen phosphorylase
The enzyme that cleaves glycogen to glucose-1-phosphate.
Glycogen synthase
The enzyme that synthesizes glycogen from UDP-glucose.
Glycosidases
Enzymes that cleave glycosidic bonds.
Glycosyl transferases
Biosynthetic enzymes that use activated monosaccharides.
glyoxysome
A specialized peroxisome containing the enzymes of the glyoxylate cycle; found in cells of germinating seeds.
GTP-binding protein
Also called GTPase; an enzyme that converts GTP to GDP.
GTPase
An enzyme that converts GTP to GDP. GTPases fall into two large families. Large trimeric G proteins are composed of three different subunits and mainly couple GPCRs to enzymes or ion channels in the plasma membrane. Small monomeric GTP-binding proteins (also called monomeric GTPases) consist of a single subunit and help relay signals from many types of cell-surface receptors and have roles in intracellular signaling pathways, regulating intracellular vesicle trafficking, and signaling to the cytoskeleton. Both trimeric G proteins and monomeric GTPases cycle between an active GTP-bound form and an inactive GDP-bound form and frequently act as molecular switches in intracellular signaling pathways.
Guanylate cyclases
Cyclic GMP-synthesizing enzymes.
heme oxygenase
A mucosal enzyme that is able to break down the heme molecule and liberate iron.
hemolysin
An enzyme that lyses red blood cells.
heterotropic enzyme
An allosteric enzyme requiring a modulator other than its substrate.
Hexokinase
The enzyme that phosphorylates glucose to glucose-6-phosphate.
homotropic enzyme
An allosteric enzyme that uses its substrate as a modulator.
hyaluronidase
An enzyme secreted by certain bacteria that hydrolyzes hyaluronic acid and helps spread microorganisms from their initial site of infection.
Hydroxylase
Enzyme that introduces a hydroxyl group into its substrate.
Hypoxanthine-guanine phosphoribosyltransferase (HPRT)
The most important salvage enzyme for purine bases.
I-cell disease
A lysosomal storage disease caused by misrouting of lysosomal enzymes.
IFN-γ-induced lysosomal thiol reductase (GILT)
An enzyme present in the endosomal compartment of many antigen-presenting cells that denatures disulfide bonds to facilitate the degradation and processing of proteins.
indoleamine 2,3-dioxygenase (IDO)
Enzyme expressed by immune cells and some tumors that catabolizes tryptophan into kynurenine metabolites that can have immunosuppressive functions.
Induced-fit model
A model that assumes a flexible substrate-binding site in the enzyme.
Inducible enzyme
An enzyme that is synthesized only in the presence of the substrate that acts as an inducer.
inorganic pyrophosphatase
An enzyme that hydrolyzes a molecule of inorganic pyrophosphate to yield two molecules of (ortho) phosphate; also known as pyrophosphatase.
Integrases
Enzymes that catalyze site-specific recombination.
intermediary metabolism
In cells, the enzyme-catalyzed reactions that extract chemical energy from nutrient molecules and use it to synthesize and assemble cell components.
International unit (IU)
The enzyme activity that converts 1 μmol of substrate to product per minute.
iodothyronine deiodinase
A selenium- containing enzyme that is involved in the conversion of thyroxin into the metabolically active triiodothyronine by removal of an iodine atom.
Irreversible inhibition
Inhibition by the formation of a covalent bond with the enzyme.
Isoenzymes
Enzymes catalyzing the same reaction but composed of different polypeptides.
juxtaglomerular apparatus
A group of kidney arteriole cells of the glomerulus that produce the enzyme renin.
koji
A microbial fermentation on rice; usually Aspergillus oryzae; used to produce amylase.
kynurenine metabolites
Various compounds derived from tryptophan through the actions of the enzymes indolamine-2,3-dioxygenase (IDO) or tryptophan-2,3-dioxygenase (TDO) expressed in various immune cells or the liver.
lactase
Digestive enzyme produced by the small intestine that splits the disaccharide lactose.
Lecithin-cholesterol acyltransferase (LCAT)
An enzyme bound to high-density lipoprotein (HDL) that converts free cholesterol into cholesterol esters.
Lipoprotein lipase
An endothelial enzyme that hydrolyzes triglycerides in chylomicrons and verylow- density lipoprotein (VLDL).
Lock-and-key model
A model that assumes a rigid substrate-binding site in the enzyme.
LoxP site
Recognition site for the DNA-splicing enzyme Cre recombinase.
luciferase
An enzyme that accepts electrons from flavoproteins and emits a photon of light in bioluminescence.
M6P receptor proteins
Transmembrane receptor proteins present in the trans Golgi network that recognize the mannose 6-phosphate (M6P) groups added exclusively to lysosomal enzymes, marking the enzymes for packaging and delivery to early endosomes.
maltase
Digestive enzyme produced by the small intestine that splits the disaccharide maltose.
matrix metalloprotease
Ca2+- or Zn2+-dependent proteolytic enzyme present in the extracellular matrix that degrades matrix proteins. Includes the collagenases.
methylase
An enzyme that attaches methyl groups (—CH3) to a molecule; methylated cytosine is protected from digestion by restriction enzymes.
methylmalonic acidemia
An inborn error of metabolism in which an enzyme needed for threonine breakdown, methylmalonyl-CoA mutase, is defective, leading to an accumulation of methylmalonic acid.
Michaelis-Menten kinetics
A kinetic pattern in which the initial rate of an enzymecatalyzed reaction exhibits a hyperbolic dependence on substrate concentration.
mixed inhibition
The reversible inhibition pattern resulting when an inhibitor molecule can bind to either the free enzyme or the enzyme-substrate complex (not necessarily with the same affinity).
mixed-function oxygenases
Enzymes (a monooxygenase, for example) that catalyze reactions in which two reductants—one of which is generally NADPH, the other the substrate—are oxidized. One oxygen atom is incorporated into the product, the other is reduced to H2O. These enzymes often use cytochrome P-450 to carry electrons from NADPH to O2.
modulator
A metabolite that, when bound to the allosteric site of an enzyme, alters its kinetic characteristics.
Monoamine oxidase (MAO)
An enzyme that inactivates catecholamines and serotonin.
monomeric GTPase
A single-subunit enzyme that converts GTP to GDP (also called small monomeric GTP-binding proteins). Cycles between an active GTP-bound form and an inactive GDP-bound form and frequently acts as a molecular switch in intracellular signaling pathways.
Monooxygenases
Enzymes that incorporate a single oxygen atom from O2 into their substrate.
moonlighting enzymes
Enzymes that play two distinct roles, at least one of which is catalytic; the other may be catalytic, regulatory, or structural.
multienzyme system
A group of related enzymes participating in a given metabolic pathway.
mutases
Enzymes that catalyze the transposition of functional groups.
myokinase
(MK)—An enzyme of the phosphagen system that takes a phosphate from an adenosine diphosphate and adds the phosphate and adenosine diphosphate to make adenosine triphosphate.
NAD+
A coenzyme that functions in the removal and transfer of hydrogen ion (H-) and electrons from substrate molecules.
NADP+
A coenzyme similar to NAD+.
NADPH oxidase
Multicomponent enzyme complex that is assembled and activated in the phagolysosome membrane in stimulated phagocytes. It generates superoxide in an oxygen-requiring reaction called the respiratory burst.
nitrogenase complex
A system of enzymes capable of reducing atmospheric nitrogen to ammonia in the presence of ATP.
NO synthase (NOS)
Enzyme that synthesizes nitric oxide (NO) by the deamination of arginine.
Noncompetitive inhibition
Inhibition by an agent that binds the enzyme noncovalently outside its active site.
noncompetitive inhibitor
An inhibitory chemical that does not compete with the substrate for an enzyme’s active site. See also allosteric inhibition; competitive inhibitor.
nucleoside diphosphate kinase
An enzyme that catalyzes the transfer of the terminal phosphate of a nucleoside 5’-triphosphate to a nucleoside 5’-diphosphate.
nucleoside diphosphate sugar
A coenzymelike carrier of a sugar molecule, functioning in the enzymatic synthesis of polysaccharides and sugar derivatives.
nucleoside monophosphate kinase
An enzyme that catalyzes the transfer of the terminal phosphate of ATP to a nucleoside 5’-monophosphate.
oligoadenylate synthetase
Enzyme produced in response to stimulation of cells by interferon. It synthesizes unusual nucleotide polymers, which in turn activate a ribonuclease that degrades viral RNA.
optimum pH
The characteristic pH at which an enzyme has maximal catalytic activity.
oxidase test
Test for an enzyme that oxidizes cytochrome c.
oxidases
Enzymes that catalyze oxidation reactions in which molecular oxygen serves as the electron acceptor, but neither of the oxygen atoms is incorporated into the product. Compare oxygenases.
Oxidoreductase
Enzyme catalyzing oxidation-reduction reactions.
Oxygen sensing
Molecular mechanisms that allow the cell to sense changes in oxygen availability and to adjust gene expression and metabolism. Oxygen sensing often involves redox sensitive transcription factors or other posttranslational modifications catalyzed by redox-regulated enzymes.
oxygenases
Enzymes that catalyze reactions in which oxygen atoms are directly incorporated into the product, forming a hydroxyl or carboxyl group. In reactions catalyzed by a monooxygenase, only one of the two O atoms is incorporated; the other is reduced to H2O. In reactions catalyzed by a dioxygenase, both O atoms are incorporated into the product. Compare oxidases.
pancreatic juice
A secretion produced by the pancreas and released into the small intestine; contains both a variety of digestive enzymes and bicarbonate (which is a weak base).
Pancreatic lipase
The major enzyme of fat digestion.
Pantothenic acid
A nutritionally essential constituent of coenzyme A.
Phosphatase-1
The enzyme that dephosphorylates glycogen synthase, glycogen phosphorylase, and phosphorylase kinase.
phosphatases
Enzymes that cleave phosphate esters by hydrolysis, the addition of the elements of water.
phosphatidylinositol 3-kinase (PI 3-kinase)
Enzyme involved in intracellular signaling pathways. It phosphorylates the membrane lipid phosphatidylinositol 3,4-bisphosphate (PIP2) to form phosphatidylinositol 3,4,5-trisphosphate (PIP3), which can recruit signaling proteins containing pleckstrin homology (PH) domains to the membrane.
phosphatidylinositol kinases
Enzymes that phosphorylate the inositol headgroup on membrane lipids to produce phosphorylated derivatives that have a variety of functions in intracellular signaling.
phosphodiesterase (PDE)
An enzyme that breaks down the cyclic nucleotide second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP).
Phosphodiesterases
Enzymes that hydrolyze cyclic AMP, cyclic GMP, or both.
Phosphoenolpyruvate (PEP) carboxykinase
A gluconeogenic enzyme that is induced by glucagon and glucocorticoids.
phosphoinositide 3-kinase (PI 3-kinase)
Membrane-bound enzyme that is a component of the PI-3-kinase–Akt intracellular signaling pathway. It phosphorylates phosphatidylinositol 4,5-bisphosphate at the 3 position on the inositol ring to produce PIP3 docking sites in the membrane for other intracellular signaling proteins.
phospholipase C-γ (PLC-γ)
Key enzyme in intracellular signaling pathways leading from many different receptors. It is activated by membrane recruitment and tyrosine phosphorylation following receptor ligation, and cleaves membrane inositol phospholipids into inositol trisphosphate and diacylglycerol.
Phospholipases
Phosphoglyceride-hydrolyzing enzymes.
Phosphopantetheine
A prosthetic group of fatty acid synthase.
Physiological responses
Changes in enzyme activities, gene expression, or growth that are a consequence of a perceived exogenous stimulus.
phytase
An enzyme that can break down the monosaccharide phytic acid and can bind up trace minerals.
Phytodegradation
Biochemical breakdown of contaminants caused by plant enzymes and plant catabolic processes.
Poly(A) polymerase
An enzyme that adds the poly(A) tails to the 3′ termini of eukaryotic gene transcripts (RNAs).
Polylinker (multiple cloning site)
A segment of DNA that contains a set of unique restriction enzyme cleavage sites.
Polymerase
An enzyme that catalyzes the formation of DNA or RNA.
porphyria
Inherited condition resulting from the lack of one or more enzymes required to synthesize porphyrins.
prochiral molecule
A symmetric molecule that can react asymmetrically with an enzyme having an asymmetric active site, generating a chiral product.
propionic acidemia
An inborn error of metabolism in which an enzyme needed for threonine catabolism, propionyl CoA carboxylase, is defective, leading to an accumulation of propionic acid.
prostatic acid phosphatase (PAP)
Enzyme expressed by prostate cancer cells used as tumor rejection antigen in the vaccine Sipuleucel-T (Provenge).
protein tyrosine phosphatase
Enzyme that removes phosphate groups from phosphorylated tyrosine residues on proteins.
purine nucleotide phosphorylase (PNP) deficiency
An enzyme defect that results in severe combined immunodeficiency. The deficiency of PNP causes an intracellular accumulation of purine nucleosides, which are toxic to developing T cells.
pyridine nucleotide
A nucleotide coenzyme containing the pyridine derivative nicotinamide; NAD or NADP.
Pyruvate carboxylase
The mitochondrial enzyme that turns pyruvate into oxaloacetate.
Pyruvate dehydrogenase
The mitochondrial enzyme complex that turns pyruvate into acetyl-CoA.
Pyruvate kinase
The glycolytic enzyme that turns phosphoenolpyruvate (PEP) into pyruvate.
regulatory enzyme
An enzyme with a regulatory function, through its capacity to undergo a change in catalytic activity by allosteric mechanisms or by covalent modification.
regulatory site
Region of an enzyme surface to which a regulatory molecule binds and thereby influences the catalytic events at the separate active site.
Restriction fragment-length polymorphism (RFLP)
The existence of two or more genetic variants detectable by visualizing fragments of genomic DNA that were obtained by digesting the DNA with a restriction enzyme. Usually the DNA fragments are fractionated by electrophoresis, transferred to a membrane by Southern blotting, and then visualized by autoradiography after hybridization to a labeled DNA probe.
Restriction map
A linear or circular physical map of a DNA molecule showing the sites that are cleaved by different restriction enzymes.
Restriction site
A DNA sequence that is cleaved by a restriction enzyme.
reversible inhibition
Inhibition by a molecule that binds reversibly to the enzyme, such that the enzyme activity returns when the inhibitor is no longer present.
RFLP
Restriction fragment length polymorphism; a fragment resulting from restriction-enzyme digestion of DNA.
Ribonuclease (RNase)
Any enzyme that hydrolyzes RNA.
Ribonucleotide reductase
The enzyme that reduces ribose to 2-deoxyribose in the nucleoside diphosphates.
RNA replicase
A viral enzyme that synthesizes RNA on an RNA template.
RNase H
An enzyme that degrades the RNA strand in a DNA-RNA hybrid.
saturation
(1) The condition in which the active site on an enzyme is occupied by the substrate or product at all times. (2) In a fatty acid, having no double bonds.
second messenger cascade
A multistep process that couples activation of a neurotransmitter receptor to activation of intracellular enzymes.
secretory phospholipase A2
Antimicrobial enzyme present in tears and saliva and also secreted by the Paneth cells of the gut.
serine/threonine kinase
Enzyme that phosphorylates specific proteins on serine or threonines.
signaling scaffold
A configuration of proteins and modifications, such as phosphorylation or ubiquitination, that facilitates signaling by binding various enzymes and their substrates.
SIRT
Groups of proteins sometimes referred to as silent information regulator 2 or Sir2. It has roles in various critical metabolic pathways by activating enzymes. It is under the control of increased levels of NAD+ that result in increased expression of SIRT.
SIRT1-AMPK-PGC1a complex
A complex whereby activity of a group of enzymes and regulatory transcription factors improves insulin sensitivity, enhanced fatty acid oxidation, and decreased lipogenesis. Dietary leucine intake may activate this complex and lead to decreased obesity.
sirtuins
Referred to as “silent information regulator 2”, works with niacin in affecting those enzymes involved with insulin secretion, gluconeogenesis, mitochondrial biogenesis, endothelial function, lipid metabolism, cell cycling, and apoptosis.
small heterodimer partner (SHP)
A gene product that inhibits the transcription of the mRNA for 7 a-hydroxylase, a rate-limiting enzyme in the conversion of cholesterol to bile acid.
specific activity
The number of micromoles (mol) of a substrate transformed by an enzyme preparation per minute per milligram of protein at 25 8C; a measure of enzyme purity.
steap3
An enzyme that removes transferrin-bound iron that has been engulfed by a liver endosome and converts it from the ferric form of iron to the ferrous form.
streptolysin
A hemolytic enzyme, produced by streptococci.
Streptomycete antibiotics
To date approximately 17% of biologically active secondary metabolites have been characterized from streptomycetes. Main sources are soil streptomycetes and marine actinomycetes including those from the genus Streptomyces (Actinobacteria). The most important environmental signal triggering secondary metabolism is nutrient starvation, particularly lack of phosphate. Effectors according to biological activity: antagonistic agents including antibacterials, antifungals, antiprotozoans, as well as antivirals, pharmacological agents including antitumorals, immunomodulators, neurological agents, and enzyme inhibitors, agrobiologicals including insecticides, pesticides, and herbicides, and compounds with regulatory activities such as growth factors, siderophores, or morphogenic agents.
substrate channeling
Movement of the chemical intermediates in a series of enzymecatalyzed reactions from the active site of one enzyme to that of the next enzyme in the pathway, without leaving the surface of a protein complex that includes both enzymes.
sucrase
Digestive enzyme produced by the small intestine that splits the disaccharide sucrose.
sucrose
Disaccharide derived from the sugar cane plant that is used as a sweetener in recipes; it is digested in the small intestine by the enzyme sucrase.
suicide inactivator
A relatively inert molecule that is transformed by an enzyme, at its active site, into a reactive substance that irreversibly inactivates the enzyme.
synthases
Enzymes that catalyze condensation reactions in which no nucleoside triphosphate is required as an energy source.
synthetases
Enzymes that catalyze condensation reactions using ATP or another nucleoside triphosphate as an energy source.
TACE (TNF-α-converting enzyme)
A protease responsible for cleavage of the membrane-associated form of TNF-α, allowing cytokine release into its soluble form that can enter the systemic circulation.
terminal deoxynucleotidyl transferase (TdT)
Enzyme that inserts nontemplated N-nucleotides into the junctions between gene segments in T-cell receptor and immunoglobulin V-region genes during their assembly.
thioredoxin reductase
Selenium containing enzymes that reduce the protein thioredoxin to reduce other compounds as part of an oxidation-reduction cycle.
Thymidylate synthase
The folate-dependent enzyme that methylates uracil to thymine in deoxyuridine monophosphate.
Transcriptomics
Global study of gene expression at the RNA level; determination of the RNA sequence by sequencing the complementary DNA (cDNA). The latter is obtained from RNA by reverse transcription using the enzyme reverse transcriptase.
Transferase
Enzyme that transfers a group between substrates.
Transglutaminase
Clotting factor XIIIa, a fibrincross- linking enzyme.
transition-state analog
A stable molecule that resembles the transition state of a particular reaction, and therefore binds the enzyme that catalyzes the reaction more tightly than does the substrate in the ES complex.
Tryptophan operon
An operon in Escherichia coli that codes for enzymes of tryptophan biosynthesis.
type I muscle fiber
Fibers that have a low force-generating capacity; also known as slow-twitch fibers. These fibers tend to be smaller, have higher concentrations of oxidative enzymes, and be more fatigue resistant than type II fibers.
type II muscle fiber
Fibers that have a high force-generating capacity; also known as fast-twitch fibers. These fibers tend to be larger, have higher concentrations of anaerobic enzymes, and be more fatigue sensitive than type I fibers. V .
tyrosine kinase
Enzyme that phosphorylates specific proteins on tyrosines. See also cytoplasmic tyrosine kinase.
tyrosine phosphatases
Enzymes that remove phosphate groups from phosphorylated tyrosine residues on proteins. See also CD45.
tyrosine protein kinases
Enzymes that specifically phosphorylate tyrosine residues in proteins. They are critical in the signaling pathways that lead to T- and B-cell activation.
tyrosinemia type II
An inborn error of metabolism in which tyrosine accumulates due to a defect in the enzyme tyrosine aminotransferase, which converts tyrosine to p-hydroxyphenol-pyruvate. Can lead to mental retardation and skin and eye lesions, if left untreated.
uncompetitive inhibition
The reversible inhibition pattern resulting when an inhibitor molecule can bind to the enzyme-substrate complex but not to the free enzyme.
uracil-DNA glycosylase (UNG)
Enzyme that removes uracil bases from DNA in a DNA repair pathway that can lead to somatic hypermutation, class switch recombination or gene conversion.
Urease
An enzyme in some bacteria and plants that cleaves urea to carbonic acid and ammonia.
viral protease
Enzyme encoded by the human immunodeficiency virus that cleaves the long polyprotein products of the viral genes into individual proteins.
Xanthine oxidase
A flavoprotein enzyme that produces uric acid.
ZAP-70 (ζ-chain-associated protein)
A cytoplasmic tyrosine kinase found in T cells that binds to the phosphorylated ζ chain of the T-cell receptor and is a key enzyme in signaling T-cell activation.
Zinc
A trace mineral in the body; constituent of many enzymes.
α-ketoadipic aciduria
A genetic defect in a gene that encodes for the enzyme α-ketoadipic dehydrogenase that converts α-ketoadipic acid to glutaryl-CoA. α-ketoadipicacid accumulates and in infants this disease can lead to difficulty with motor skills and may have seizures.
β-Galactosidase
A lactose-hydrolyzing enzyme.
β-Lactamase
Penicillinase; an enzyme that inactivates penicillin and related antibiotics.
