Chapter 7 The mechanisms of chemical catalysis used by enzymes

Abstract

Publisher Summary This chapter discusses the mechanisms of chemical catalysis used by enzymes. Although enzymes may contain several hundred amino acid residues, only two or three of them are chemically involved in the bond -making and -breaking steps in the transformation catalyzed by the enzyme. The main purpose of the bulk of the amino acid residues is to provide the fairly rigid three-dimensional framework required to maximize the binding energy between substrate and enzyme. Majority of the reactions involve a redistribution of electron density on going from the ground state to the transition state. The function of catalytic groups on the enzyme or coenzyme is to stabilize these electron-density changes or to provide an alternative pathway for the reaction. Charge complementarity is an extension of Pauling's electroneutrality principle. Electron-rich nucleophiles, bases, and reducing agents are paired with electron-deficient electrophiles, acids, and oxidizing agents, respectively. Charge may also be stabilized by delocalization. This principle also extends to the resting enzyme. In the absence of substrate, the electron distribution of groups within the enzyme is neutralized, as allowed by the three-dimensional framework, by complementary groups or solvent.