Lecture: Enzymology Flashcards
Protein part of an enzyme without the cofactor necessary for catalysis
Apoenzyme
An effector molecule that increases the catalytic activity of an enzyme when it binds to a specific site
Activator
Substance that diminishes the rate of a chemical reaction
Inhibitor
Property of a catalyst that is measured by the catalyzed rate of conversion of a specified chemical reaction produced in a specified assay system
Catalytic Activity
When combined with an inactive protein called an apoenzyme, forms an active compound (complete enzyme) called a holoenzyme
Coenzyme
A protein molecule that catalyzes chemical reaction without itself being destroyed, altered, consumed
Enzyme
Group of related enzymes catalyzing the same reaction but having different molecular structures and physical, biochemical, and immunological properties
Isoenzyme
Amount of enzyme that catalyzes the conversion of one micromole of substrate per minute under the specified conditions of the assay method
International Unit
A reactant in a catalyzed reaction
Substrate
Substance produced by the enzyme-catalyzed conversion of a substrate
Product
Water-free cavity; specific portion of enzyme that binds on the substrate
Active Site
A cavity other than the active site which may bind with regulatory molecules
Allosteric Site
When bound tightly to the enzyme, the coenzyme is called
Prosthetic group
Digestive enzyme originally secreted from the organ of production is called a
Proenzyme
Zymogen
Apoenzyme and coenzyme forms a complete and active system known
Holoenzyme
Enzyme have a rigid active site; The shape of the key (substrate) must fit into the lock (enzyme)
Emil Fisher’s / Lock and Key Theory
Enzyme has a flexible active site; Based on the substrate binding to the active site of the enzyme
Kochland / Induced Fit Theory
The minimum energy input needed for a reaction to occur and convert the substrates into products
Activation Energy
A molecular intermediate between the substrate and its product, through which the reaction passes
Transition State
Enzymes work by _ activation energy
Lowering
An enzyme combines with only one substrate and catalyzes only one reaction
Absolute Specificity
Enzymes combine with all the substrates in a chemical group
Group Specificity
Enzymes reacting with specific chemical bonds
Bond Specificity
Isoenzymes/isoforms
Stereoisomers
If the reaction reached the maximum velocity, no reaction will happen.
Michaelis Menten Kinetics
Reaction rate depends only on enzyme concentration
Zero-Order Reaction
Reaction rate is directly proportional to the substrate concentration
First-Order Reaction
The rate of reaction depends on the doubled concentration of one reactant or on the product of concentration of two reactants
Second-Order Reaction
6 Enzyme Nomenclature
Oxidoreductases
Transferases
Hydrolases
Lyases
Isomerases
Ligases
Catalyzes the transfer of electrons from 1 molecule (oxidant) to another molecule (reductant)
Oxidoreductases
Oxidoreductases often requires cofactors such as _
NADPH
Add hydroxyl groups to a substrate
Hydroxylases
Intramolecular oxygen is the hydrogen or electron acceptor
Oxidases
Oxidize a substrate by transferring one or more hydride ion
Dehydrogenase
Reduction of hydrogen peroxide and organic hydroperoxides
Peroxidase
Catalyze reductions
Reductase
Incorporate intramolecular oxygen into organic substrates
Oxygenase
Enzymes that catalyze the movement of a functional group from one molecule to another
Transferases
Enzymes are involved in catalyzing the transfer of phosphate groups in a process called phosphorylation
Kinase
Enzymes that catalyzes the transfer an amine group
Deaminases
Catalyzes hydrolysis (breaking of single bonds through the addition of water)
Hydrolase
Catalyzes lysis reactions that generate a double bond; type of elimination reaction but not hydrolytic or oxidative; often referred to as synthase enzymes
Lyases
Catalyzes addition reaction (substrate is added to a double bond)
Reverse Reaction
Enzymes that catalyzes structural changes within a molecule
Isomerases
Joining enzymes; responsible for catalyzing ligation of 2 molecules with the hydrolysis of a diphosphate bond in ATP or any triphosphate
Ligases
Associated with a unique numerical code designation
Enzyme Commission Numerical Nomenclature
First EC Digit of oxidoreductases
1
First EC Digit of transferases
2
First EC Digit of hydrolases
3
First EC Digit of lyases
4
First EC Digit of isomerases
5
First EC Digit of ligases
6
The temperature at which the enzyme is most active, catalyzing the largest number of reactions per second
Optimum Temperature
Most enzymes in the human body function best at about _
37 degrees Celsius
The rate of denaturation increases as the temperature increases and is usually significant at
40°C to 50°C
Looser, more random structure, and become insoluble
Denatured proteins
The process where the enzyme loses its shape and active site
Denaturation
Low temperature or freezing does not usually destroy enzymes, except:
LD – freezing at -20 degrees C
CK – storing at 4 degrees C
Enzymes that work best at acidic conditions
Renin and pepsin
Enzymes that work best at alkaline conditions
Intestinal enzymes
Enzymes that work best at neutral conditions
Amylase
At pH slightly above or below the optimum, enzyme activity _
Reduces
At extreme pH conditions, enzymes are _
Denatured
Physically bind to the active site of an enzyme and compete with the substrate for the active site; reversible
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
Another kind of inhibition in which the inhibitor binds to the ES complex
Uncompetitive inhibition
Reaction takes place at a certain period; reactions are combined; reaction proceeds for a designated time; reaction is assumed to be linear over the reaction time; the larger the reaction, the more enzyme is present
Fixed-Time (Endpoint Method)
Measured absorbance at a certain period; More advantageous than fixed time – allows monitoring of linearity
Continuous Monitoring (Kinetic Assay)
Amount of enzyme that catalyzes 1 micromole of substrate per minute
International Unit (IU/U)
1 mole of substrate per second
Katal Unit (KU)
