Chapter 2 - Enzymes

Abstract

Publisher Summary This chapter provides an overview of enzymes. Enzymes are the machine tools that have the ability to split complicated molecules apart at predetermined sites and to assemble required metabolites by joining simpler atoms or molecules together. Output is shut off at the required level by means of a feedback system similar to that in an ordinary thermostat. Enzymes, therefore, have a key position in cellular and somatic organization. They resemble chemical catalysts in their ability to assist the mechanisms used in bodily metabolism without themselves being used up in the process. Examples of such biological catalysis are the hydrolysis of peptide linkages, the transfer of carboxyl groups, the splitting of carbon-to-carbon bonds, and the transformation of substances into their optical, positional, or geometric isomeric forms. In all these and many other processes, enzymes may function alone or with the assistance of cofactors. In the latter case, the active enzyme or holoenzyme is a complex of two parts, the apoenzyme or protein part, and a smaller cofactoral element. The apoenzyme is powerless to act on its own. The cofactor may be a divalent or trivalent cation, when it is called an activator, or it may be a complicated organic molecule, usually a vitamin derivative, when it is customary to refer to it as a coenzyme. Either or both may be required for full enzymic action in specific instances. The chapter discusses isoenzymes, pre-enzymes, intracellular localization of enzymes, enzyme synthesis, enzyme structure, enzyme cofactors, enzyme specificity, rate of enzyme reactions, enzyme inhibition, antienzymes, and enzyme nomenclature.