Enzymes Flashcards
specific biologic proteins that catalyze biochemical reactions
without altering the equilibrium point of the reaction or being consumed or
changed in composition.
Enzymes
The different forms may be differentiated from each other based on
certain physical properties, such as electrophoretic mobility, solubility, or
resistance to inactivation.
isoenzyme
results when an enzyme is subject to posttranslational modifications.
isoform
a nonprotein molecule, called a
_____, may be necessary for enzyme activity.
cofactor
Inorganic cofactors, such as
chloride or magnesium ions, are called
activators.
is an organic
cofactor, such as nicotinamide adenine dinucleotide (NAD).
coenzyme
When bound tightly
to the enzyme, the coenzyme is called a
prosthetic group.
The enzyme portion ______, with its respective coenzyme, forms a complete and active
system, a ______.
apoenzyme; holoenzyme
Catalyze an oxidation–reduction reaction between two
substrates
Oxidoreductases.
Catalyze the transfer of a group other than hydrogen from
one substrate to another
Transferases.
Catalyze hydrolysis of various bonds
Hydrolases.
Catalyze removal of groups from substrates without hydrolysis; the
product contains double bonds
Lyases.
Catalyze the interconversion of geometric, optical, or
positional isomers
Isomerases.
Catalyze the joining of two substrate molecules, coupled with
breaking of the pyrophosphate bond in adenosine triphosphate (ATP) or a
similar compound
Ligases.
The excess energy, called
_________, is the energy required to raise all molecules in 1 mole of a
compound at a certain temperature to the transition state at the peak of the
energy barrier.
activation energy
refers to enzymes that predominantly combine
with only one optical isomer of a certain compound.
Stereoisomeric specificity
the reaction rate is
directly proportional to substrate concentration.
first-order kinetics
the reaction rate depends only on enzyme
concentration.
zero-order kinetics
is the substrate concentration at which
the reaction velocity is half of the maximum level.
Michaelis-Menten constant (Km)
more accurate and convenient
determination of Vmax and Km may be made through a ____________, a
double-reciprocal plot of the Michaelis-Menten constant,
Lineweaver-Burk plot
For each __ degree increase in temperature, the rate
of the reaction will approximately double
10
The rate of denaturation increases as the temperature
increases and is usually significant at
40°C to 50°C.
physically bind to
the active site of an enzyme and compete with the substrate for the active site.
Competitive inhibitors
binds an enzyme at a place other than the active
site and may be reversible in the respect that some naturally present metabolic
substances combine reversibly with certain enzymes.
noncompetitive inhibitor
the inhibitor
binds to the ES complex—increasing substrate concentration results in more ES
complexes to which the inhibitor binds and, thereby, increases the inhibition.
Uncompetitive inhibition
has the ability to bind to either the E or ES complex at a different site
from the substrate active site.
mixed
inhibitor
Vmax
unaltered; Km appears increased.
Competitive inhibition
Vmax decreased;
Km unchanged.
Noncompetitive inhibition
Vmax decreased; Km appears
decreased.
Uncompetitive inhibition
a convenient method of
enzyme quantitation is measurement of
catalytic activity.
One of two general methods may be used to measure the extent of an
enzymatic reaction:
fixed-time and continuous-monitoring or kinetic assay
the reactants are combined, the reaction
proceeds for a designated time, the reaction is stopped (usually by inactivating
the enzyme with a weak acid), and a measurement is made of the amount of
reaction that has occurred.
fixed-time method,
multiple measurements, usually
of absorbance change, are made during the reaction, either at specific time
intervals (usually every 30 or 60 seconds) or continuously by a continuous-
recording spectrophotometer.
continuous-monitoring or kinetic assays,
the amount of enzyme that will catalyze the reaction of 1 μmol of
substrate per minute under specified conditions of temperature, pH, substrates,
and activators.
international unit (IU)
specific. Enzyme concentration is
usually expressed in units per liter (IU/L). The unit of enzyme activity
recognized by the International System of Units (Système International d’Unités
[SI]) is the
katal (mol/s).
are chemically bonded to adsorbents, such as agarose
or certain types of cellulose, by azide groups, diazo, and triazine.
Immobilized enzymes
widely distributed in tissue, with highest activities found in skeletal
muscle, heart muscle, and brain tissue.
CK
Total serum CK levels have also been used as an early diagnostic tool to identify
patients with_____ infections.
Vibrio vulnificus
useful in the diagnosis of ectopic pregnancies.
and
CK/progesterone ratio
The major isoenzyme in the sera of healthy people is the
MM form.
<6% of total CK
CK-MB
atypical forms are
generally of two types (CK)
macro-CK and mitochondrial CK.
appears to migrate to a position midway between CK-MM and
CK-MB. comprises CK-BB complexed with
immunoglobulin.
macro-CK
bound to the exterior surface of the inner
mitochondrial membranes of muscle, brain, and liver. It migrates to a point
cathodal to CK-MM and exists as a dimeric molecule of two identical subunits.
Mitochondrial CK (CK-Mi)
is an enzyme released from
erythrocytes in hemolyzed samples and appearing as a band cathodal to CK-
MM.
adenylate kinase (AK).
the most
commonly performed method in the clinical laboratory for CK
Oliver-Rosalki (reverse method)
enzyme that catalyzes the interconversion of lactic and pyruvic acids.
Lactate Dehydrogenase
occur most frequently with pulmonary
involvement and are also observed in patients with various carcinomas.
Elevations of LDH-3
isoenzymes are found primarily in liver and skeletal muscle
tissue
LDH-4 and LDH-5
functions as a coenzyme in SGOT/SGPT
Pyridoxal phosphate (B6)
Half-life of AST
16hrs
Half-life of ALT
24hrs
belongs to a group of enzymes that catalyze the hydrolysis of various
phosphomonoesters at an alkaline pH.
Alkaline Phosphatase
ALP requires ___ as an activator
Mg2+
Migration pattern of ALP: fastest to slowest
Liver
Bone
Placental
Intestine
Most heat stable to heat labile
Placental
Intestinal
Liver
Bone
Placental ALP will resist heat denaturation at
65°C for 30 minutes.
ALP activity is measured
before and after heating the serum at
56°C for 10mins
The most frequently seen are the Regan
and Nagao isoenzymes. They have been referred to as
carcinoplacental alkaline
phosphatases
migrates to the same position as the bone fraction and
is the most heat stable of all ALP isoenzymes, resisting denaturation at 65°C for
30 minutes. Its activity is inhibited by phenylalanine.
Regan isoenzyme
may be considered a variant of the Regan isoenzyme.
Its electrophoretic, heat stability, and phenylalanine inhibition properties are
identical to those of the Regan fraction.
Nagao isoenzyme
Nagao also can be inhibited by
L-leucine
A continuous monitoring
technique based on a method devised by _______ allows
calculation of ALP activity based on the molar absorptivity of p-nitrophenol.
Bowers and McComb
ALP Activity in serum increases approximately _____ on standing at 25°C or 4°C for several hours.
3%
to 10%
ALP Values
may be ___ higher following ingestion of a high-fat meal.
25%
3 approaches to identify ALP isoenzymes
Electrophoresis
Heat Inactivation
Chemical inhibition
One of the most specific substrates for prostatic ACP is
thymolphthalein
monophosphate.
Chemical inhibition methods used to differentiate the prostatic
portion most frequently use ____ as the inhibitor.
tartrate
Vaginal washings are examined for seminal fluid–ACP
activity, which can persist for up to __ days
4
includes incubation with an antibody to
prostatic ACP followed by washing and incubation with p-nitrophenylphosphate.
immunoenzymatic assay (Tandem E)
Serum activity decreases within
____ if the sample is left at room temperature without the addition of a
preservative.
1 to 2 hours
If not assayed immediately, serum should
be
frozen or acidified (<6.5)
involved in peptide and protein synthesis,
regulation of tissue glutathione levels, and the transport of amino acids across
cell membranes.
GGT
GGT levels will be increased in patients receiving enzyme-
inducing drugs such as
warfarin, phenobarbital, and phenytoin.
TRUE/FALSE: GGT Levels usually return to normal within 2 to 3 weeks
after cessation but can rise again if alcohol consumption is resumed.
TRUE
most widely accepted substrate for use in GGT analysis is
γ-glutamyl-p-
nitroanilide.
TRUE/FALSE: Hemolysis
does not interfere with GGT levels because the enzyme is lacking in
erythrocytes.
TRUE
an enzyme belonging to the class of hydrolases that catalyze the breakdown of starch and glycogen.
Amylase (AMY)
condition that results when the AMY molecule combines
with immunoglobulins to form a complex that is too large to be filtered across
the glomerulus.
Macroamylasemia
2 major bands of amylase
P-type and S-type isoamylase
derived from pancreatic tissue;
P isoamylase
derived from salivary gland tissue, as well as the fallopian tube
and lung.
S isoamylase
TRUE/FALSE: The isoenzymes of salivary origin (S1, S2, S3) migrate most quickly,
whereas those of pancreatic origin (P1, P2, P3) are slower.
TRUE
The most commonly observed fractions of amylase are
P2, S1, and S2.
Amylase methodologies: Measures the disappearance of starch substrate
Amyloclastic
Amylase methodologies: Measures the appearance of the product
Saccharogenic
Amylase methodologies: Measures the increasing color from production of product coupled with a chromogenic dye
Chromogenic
Amylase methodologies: Coupling of several enzyme systems to monitor amylase activity
Continuous monitoring
TRUE/FALSE: plasma triglycerides
suppress or inhibit serum AMY activity, AMY values may be normal in acute
pancreatitis with hyperlipemia.
TRUE
enzyme that hydrolyzes the ester linkages of fats to produce
alcohols and fatty acids.
Lipase (LPS)
used an olive oil substrate and measured the liberated fatty acids by
titration after a 24-hour incubation.
Cherry-Crandall
method
an oxidoreductase that
catalyzes the oxidation of glucose-6-phosphate to 6-phosphogluconate or the
corresponding lactone.
Glucose-6-phosphate dehydrogenase (G-6-PD)
ACP,
ALP, ALT, amylase, AST, CK, GGT, LDH, lipase
Macroenzymes
are high-molecular-mass forms of the serum enzymes that can be bound to either an immunoglobulin (macroenzyme type 1) or a nonimmunoglobulin substance
(macroenzyme type 2).
Macroenzymes
superfamily of isoenzymes that are involved in the
metabolism of more than 50% of all drugs.
450 enzymes
