Introduction to Enzymology

Vocabulary flashcards covering the fundamentals of enzymology, enzyme types, classification, kinetics, and measurement techniques.

Enzymology

The study of enzymes, including their activity, the chemical reactions they catalyze, and their clinical uses.

Biologic Catalysts

Enzymes that hasten chemical reactions without being consumed or undergoing chemical changes after the reactions.

Substrate

The specific substance acted upon by an enzyme.

Isoenzyme

A different form of an enzyme that performs the same action.

Cofactor

A non-protein molecule that may be necessary for enzyme activity; includes activators and coenzymes.

Activator

An inorganic cofactor used for proper substrate binding or to link the substrate to the enzyme or coenzyme.

Coenzyme

An organic cofactor, such as nucleotide phosphates and vitamins.

Prosthetic group

A coenzyme that is bound tightly to an enzyme.

Holoenzyme

The complete, active enzyme formed by the combination of an apoenzyme and a coenzyme.

Apoenzyme

The polypeptide or enzyme portion of a holoenzyme.

Proenzyme (Zymogen)

The inactive form of an enzyme that is converted to the active form, usually by proteolysis, upon reaching the site of activity.

Absolute Specificity

An enzyme specificity where the enzyme recognizes and catalyzes only a single substrate.

Group Specificity

An enzyme specificity where the enzyme recognizes a group of substrates that have specific functional groups.

Link Specificity

An enzyme specificity where the enzyme recognizes a group of substrates that have a particular type of bond.

Stereoisometric Specificity

An enzyme specificity where the enzyme recognizes only a particular optical isomer.

Hydrolase

An enzyme that catalyzes the hydrolysis of various bonds by adding water.

Dehydrogenase

An enzyme responsible for the removal of hydrogen atoms.

Decarboxylase

An enzyme responsible for the removal of carboxyl groups.

Oxidoreductases (E.C. 1)

Enzymes that catalyze oxidation (removal of $H^+$) and reduction (acceptance of $H^+$) reactions.

Transferases (E.C. 2)

Enzymes that catalyze the transfer of functional groups other than hydrogen from one substrate to another.

Lyases (E.C. 4)

Enzymes that catalyze the removal of groups from substrates without hydrolysis or oxidation, resulting in products with double bonds or a ring.

Isomerases (E.C. 5)

Enzymes that rearrange functional groups within a molecule to convert one isomer into another.

Ligases (E.C. 6)

Enzymes that catalyze the joining of two large molecules by forming a new chemical bond, accompanied by ATP-ADP interconversion.

Michaelis - Menten Theory

A fundamental theory of enzyme kinetics represented by the equation $E + S \rightarrow E - S \rightarrow P + E$.

Lineweaver-Burk Plot

A double-reciprocal plot of the Michaelis-Menten constant that yields a straight line.

First-Order Reactions

Reactions that proceed at a rate exactly proportional to the substrate concentration.

Zero-Order Reactions

Reactions where the substrate concentration is high enough to saturate all available enzymes, resulting in a rate independent of substrate concentration.

Vmax

The maximum reaction velocity achieved when all enzymes are saturated with substrate.

Allopurinol

A therapeutic inhibitor that targets Xanthine Oxidase for the treatment of Gout.

Aspirin

A therapeutic inhibitor that targets Cyclooxygenase to act as an anti-inflammatory agent.

5-Fluorouracil

A therapeutic inhibitor that targets Thymidylate Synthetase to act as an antineoplastic agent.

Lovastatin

A therapeutic inhibitor that targets HMG-CoA Reductase to act as a cholesterol-lowering agent.

Induced Fit

The change in the shape of an active site to fit a substrate, such as when Lysozyme binds to a bacterial polysaccharide coating.

Coupled – Enzyme Assay

An indirect measurement method where the activity of the enzyme being tested is linked to another more easily detectable enzyme.

Fixed – Time Method (End – Point)

A measurement method where reactants are combined and the reaction proceeds for a designated time before being stopped and measured.

Continuous – Monitoring Method (Kinetic Assay)

A measurement method involving multiple measurements of absorbance change (increasing or decreasing) over time.

International Unit (IU)

The amount of enzyme that will catalyze the reaction of $1\text{ micromole}$ of substrate per minute under specified conditions.

Katal Unit (kat)

The SI unit for enzyme activity, defined as the amount of enzyme that catalyzes the reaction of $1\text{ mole}$ of substrate per second; $1.0\text{ IU} = 16.7\text{ nkat}$.