Summary

Abstract

Altogether, the six tables of Chapters 2–7 list a grand total of 465 enzymes, each of which during its catalytic cycle forms a covalent bond with its substrate or some fragment of it. These long lists of enzymes point the contrast between the abundance of positive evidence for covalent catalysis and the total dearth of positive evidence for single-displacement catalysis (1). How these enzymes are apportioned among the six major classes of enzymes recognized by the Enzyme Commission (hereinafter referred to as the EC enzymes) is shown in Table 8.1 at the end of this chapter. It is clear that at least 21% of all the EC enzymes effect their catalysis through covalent enzyme-substrate intermediates. This figure assumes an even greater significance when it is realized that the vast majority of the 2200 EC enzymes have never been investigated from the standpoint of chemical mechanism. Prior to the survey embodied in the tables of Chapters 2–7, the prevalence of so much covalent catalysis by enzymes was hardly suspected.