ENZYME KINETICS AND ALLOSTERIC REGULATION IN METABOLIC PATHWAYS: MECHANISMS, MODELS, AND BIOCHEMICAL SIGNIFICANCE

Enzymes are the central catalytic agents of biochemical metabolism, and their kinetic behavior governs the rate, directionality, and regulation of virtually all metabolic pathways. This article reviews the biochemical foundations of enzyme kinetics, from the Michaelis–Menten model and its underlying assumptions to the more complex sigmoidal kinetics exhibited by allosteric enzymes. Special emphasis is placed on the molecular mechanisms of allosteric regulation, including conformational transitions described by the Monod–Wyman–Changeux (MWC) and Koshland–Nemethy–Filmer (KNF) models. The roles of key regulatory enzymes—phosphofructokinase-1 (PFK-1) in glycolysis and aspartate transcarbamoylase (ATCase) in pyrimidine biosynthesis—are analyzed as representative examples. Experimental kinetic data are discussed in the context of substrate cooperativity, feedback inhibition, and covalent modification. The article synthesizes data from eight primary biochemical research sources to provide a rigorous mechanistic account of enzyme regulation in cellular metabolism. Understanding enzyme kinetics at this depth is indispensable for drug design, metabolic engineering, and the diagnosis of inherited enzyme deficiencies.