Chapter 6: Enzymes: Kinetics, Catalytic Mechanisms, and Regulatory Control

Section 6.1 explains enzyme specificity, the nature of the active site, and substrate recognition through lock-and-key and induced-fit models. Section 6.2 details enzyme classification, dividing them into six major classes—oxidoreductases, transferases, hydrolases, lyases, isomerases, and ligases—based on the type of chemical reaction catalyzed. Section 6.3 introduces the concept of enzymatic reaction kinetics, focusing on the Michaelis-Menten equation, which relates reaction velocity (v) to substrate concentration [S]. The parameters Vmax (maximum velocity) and Km (Michaelis constant) are explained, offering insight into enzyme efficiency and substrate affinity. Lineweaver-Burk plots and other graphical methods are introduced for experimentally determining kinetic constants. Section 6.4 explores the mechanisms of enzyme catalysis, including general acid-base catalysis, covalent catalysis, metal ion catalysis, and electrostatic stabilization, and how transition state stabilization is key to catalytic power. Section 6.5 introduces enzyme inhibition, distinguishing between reversible inhibitors (competitive, uncompetitive, and mixed) and irreversible inhibitors, and explains their effects on Km and Vmax. Section 6.6 examines the role of cofactors and coenzymes such as metal ions and vitamins, many of which act as essential participants in enzymatic reactions. Finally, Section 6.7 addresses regulation of enzyme activity via allosteric control, covalent modification (e.g., phosphorylation), proteolytic activation, and feedback inhibition. This chapter lays the biochemical groundwork for understanding how enzymes function at the molecular level and how their catalytic efficiency and regulation are central to cellular metabolism and control.