Biochem Inhibitions Dive

Definition of an Enzyme

A biological catalyst that speeds up a chemical reaction without being consumed

Vmax (Maximum Velocity)

The maximum reaction rate when all active sites are saturated

Km (Michaelis constant)

Substrate concentration at which the reaction rate is half of Vmax

Relationship between Km and affinity

Lower Km = higher affinity for substrate

Competitive Inhibition

Binds to active site; increases Km; Vmax unchanged

Noncompetitive Inhibition

Binds to allosteric site; decreases Vmax; Km unchanged

Uncompetitive Inhibition

Binds only to enzyme-substrate complex; decreases both Km and Vmax

Mixed Inhibition

Binds to enzyme or ES complex; Vmax always decreases; Km can increase or decrease

Lineweaver-Burk Plot

Graph of 1/[S] vs. 1/V; straight-line form of Michaelis-Menten equation

Competitive inhibition effect on Lineweaver-Burk

Lines intersect at the y-axis (Vmax unchanged)

Noncompetitive inhibition effect on Lineweaver-Burk

Lines intersect left of y-axis; Vmax decreases, Km same

Uncompetitive inhibition effect on Lineweaver-Burk

Parallel lines; both Km and Vmax decrease

Irreversible Inhibition

Permanently disables enzyme (e.g., covalent modification)

Cofactor

A non-protein molecule required for enzyme activity (e.g., metal ions)

Coenzyme

Organic cofactor (e.g., NAD⁺, FAD, CoA)

Allosteric Regulation

Enzyme activity modified by binding at a site other than active site

Zymogen

Inactive enzyme precursor that requires cleavage to become active (e.g., trypsinogen)