Introduction to Enzymology Lecture Notes

Comprehensive vocabulary flashcards covering the Introduction to Enzymology lecture, including enzyme classifications, kinetics, factors affecting activity, and types of inhibition.

Enzymes

Biological catalysts that speed up chemical reaction by lowering activation energy.

Cofactor

The non-protein component required by some enzymes to be functional; it could be inorganic ions or an organic molecule (coenzyme).

Coenzyme

An organic molecule required by some enzymes to be functional.

Proenzyme (Zymogen)

An inactive enzyme without a cofactor (non protein part).

Prosthetic group

A cofactor (a metal ion or a coenzyme) that is very tightly or even covalently bound to the protein component of the enzyme.

EC 3.2.1.1: First Digit (3)

Represents the major Class of general reaction, in this case, Hydrolase.

EC 3.2.1.1: Second Digit (2)

Represents the Subclass of enzyme reaction, such as glycosidase.

EC 3.2.1.1: Third Digit (1)

Represents the Sub-Subclass of enzyme reaction, such as hydrolyzing O glycosyl groups.

EC 3.2.1.1: Fourth Digit (1)

Indicates the specific enzyme, such as Alpha Amylase.

Six major Class of Enzyme

1. Oxidoreductases, 2. Transferases, 3. Hydrolases, 4. Lyases, 5. Isomerases, 6. Ligases.

Fisher's Lock and Key Model

A model of enzyme action mechanism where the substrate fits into the enzyme's active site precisely.

Induced fit model of Koshland

A model of enzyme action mechanism describing the transition state of the ES complex.

Absolute substrate specificity

Describes enzymes that act on only one substrate and catalyze one reaction, such as Glucokinase, lactase, and urease.

Group specificity

A type of relative substrate specificity where an enzyme acts on more than one substrate containing a particular group; for example, chymotrypsin acting on peptide bonds attached to aromatic amino acids.

Bond specificity

A type of relative substrate specificity where an enzyme acts on more than one substrate containing a particular kind of bond; for example, salivary $\alpha$-(1$\rightarrow$4) glycosidic bonds.

Broad substrate specificity

When an enzyme acts on more than one structurally related substrates, such as hexokinase acting on all hexoses.

Reaction specificity

When an enzyme is specific to a particular reaction but not to the substrate, catalyzing only one type of reaction (e.g., pyruvate undergoing different reactions via different enzymes).

Stereo Specificity

Specificity towards stereoisomers where an enzyme acts on only one type of isomer, such as L-lactate dehydrogenase acting only on L-lactic acid.

Optimum pH

The specific hydrogen ion concentration at which the velocity of an enzyme is maximum.

Optimum temperature

The particular temperature at which an enzyme shows its highest activity.

Enzyme kinetics

The study of enzyme reaction rates and how they change following changes in experimental parameters.

Michaelis Menten equation

Describes how reaction velocity varies with substrate concentration: $V_0 = \frac{V_{max}[S]}{K_{m} + [S]}$.

$K_m$ (Michaelis Constant)

The substrate concentration at which the reaction rate is half of its maximum velocity ($V_{max}$).

Low $K_m$

Indicates a high affinity of the enzyme for its substrate.

High $K_m$

Indicates a low affinity of the enzyme for its substrate.

Lineweaver-Burk Plot

A Double-Reciprocal Plot of $1/V_0$ against $1/[S]$ used for a more accurate determination of $V_{max}$ and $K_m$.

Intercept at the x-axis (Lineweaver-Burk)

Represents $-1/K_m$.

Intercept at the y-axis (Lineweaver-Burk)

Represents $1/V_{max}$.

Allosteric regulation

The activation or inhibition of an enzyme by effector molecules.

Covalent modification

A process affecting enzyme activity where a phosphoryl group or a fatty acyl (lipid) group is added to the enzyme.

Reversible inhibition

Inhibition where inhibitors bind through non-covalent bonds and activity is fully restored once the inhibitor is removed.

Competitive Inhibitor

A structural analogue of the substrate that binds at the active site, increasing $K_m$ while leaving $V_{max}$ unchanged.

Noncompetitive Inhibitors

Inhibitors that bind at a site other than the substrate-binding site; the $K_m$ value remains unchanged while $V_{max}$ is lowered.

Uncompetitive Inhibitor

An inhibitor that binds only to the enzyme-substrate (ES) complex, decreasing both $V_{max}$ and $K_m$.

Irreversible inhibition

Inhibition due to covalent binding of the inhibitor to the enzyme or destruction of a functional group essential for its activity.

Di-isopropylphosphofluoride (DIPF)

A group specific inhibitor that covalently reacts with the hydroxyl group of a serine residue in the active site of acetylcholinesterase.

Substrate Analogue (e.g., BAP)

Molecules resembling the substrate that possess a highly reactive group which covalently reacts with amino acid residues in the active site.

Suicide Inhibitor

An inhibitor biotransformed by the enzyme into a more reactive compound that combines irreversibly with the enzyme, such as allopurinol converting to alloxanthine.