Enzymology

A mathematical model describing the rate of enzymatic reactions as a function of substrate concentration. It defines two key parameters: Vmax (the maximum reaction velocity at saturating substrate) and Km (the substrate concentration at which the reaction rate is half of Vmax).

A specific three-dimensional region of an enzyme where substrate molecules bind and undergo chemical transformation. The active site is formed by amino acid residues that may be far apart in the primary sequence but are brought together by protein folding.

The reduction of enzyme activity by molecules called inhibitors. Inhibition can be reversible (competitive, uncompetitive, noncompetitive, or mixed) or irreversible, and understanding inhibition is crucial for drug design and metabolic regulation.

The modulation of enzyme activity through the binding of effector molecules at a site other than the active site, causing conformational changes that alter catalytic function. Allosteric enzymes often exhibit sigmoidal kinetics rather than hyperbolic Michaelis-Menten kinetics.

The ability of an enzyme to select a particular substrate or type of reaction from among many possibilities. Specificity arises from the complementary shape, charge, and hydrophobic character of the active site and substrate.

Non-protein chemical compounds required by many enzymes for catalytic activity. Metal ion cofactors (e.g., Zn2+, Mg2+, Fe2+) and organic coenzymes (often derived from vitamins, e.g., NAD+, FAD, coenzyme A) participate directly in the catalytic mechanism.

The concept that enzymes accelerate reactions by preferentially binding and stabilizing the transition state of the reaction, the highest-energy intermediate along the reaction coordinate. This stabilization lowers the activation energy barrier.

The catalytic constant kcat (turnover number) represents the maximum number of substrate molecules converted to product per enzyme molecule per unit time. The ratio kcat/Km, known as the catalytic efficiency or specificity constant, measures how efficiently an enzyme converts substrate at low concentrations.

The regulation of enzyme activity through the addition or removal of chemical groups, most commonly phosphorylation. Protein kinases add phosphate groups while phosphatases remove them, acting as molecular switches that control metabolic pathways and signaling cascades.

A refinement of the lock-and-key model proposed by Daniel Koshland, stating that the active site of an enzyme is not a rigid structure but rather undergoes a conformational change upon substrate binding to achieve optimal complementarity for catalysis.