Enzymes

Abstract

Enzymes are specific protein catalysts in biological systems, which regulate the rate of biochemical and physiological processes. A catalyst is a substance that increases the rate of a chemical reaction and remains unchanged after the reaction. Coenzymes are essential for the activity of enzymes and are mainly derivatives of vitamins and AMP. Cofactor is a nonprotein metal ion associated with enzyme that is also essential for the activity of the enzyme. Zn²⁺ is associated with carbonic anhydrase and alcohol dehydrogenase, Cu²⁺ is associated with cytochrome oxidase, Mg²⁺ is associated with hexokinase and pyruvate kinase, etc. Carbonic anhydrase is one of the fastest enzymes. Apart from catalytic power, carbonic anhydrase takes part in the regulation of pH, carboxylation reaction, and CO₂ transport. Enzyme molecules contain active sites, are highly specific, and catalyze only one type of chemical reaction. Enzymes can be activated or inhibited. Allosteric enzymes can be inhibited by an inhibitor, which is not an analogue (e.g., cholesterol inhibits HMG-CoA reductase). Trypsin inhibitors are present in many vegetables, are denatured and inactivated by cooking. Lead inhibits ferrochelatase by noncompetitive inhibition and prevents the incorporation of ferrous ion into protoporphyrin for forming heme. Similarly, lead inhibits δ-aminolevulinate dehydrogenase and prevents the conversion of ALA into porphobilinogen. Velocity or rate of enzyme reaction depends on optimum temperature and pH. Michaelis–Menten equation explains the kinetic properties of the enzymes.