Approaches to Kinetic Mechanism: An Overview

Abstract

The order of addition of substrates to and release of products from the enzyme active site, along with establishment of relative rates of various events, defines the kinetic mechanism. These mechanisms fall into two broad groups – those where the full complement of substrates have to assemble on the enzyme active site before the reaction occurs are termed “sequential mechanisms.” In the other category, a product(s) is released between additions of two substrates and are called “ping–pong mechanisms.” In this category, substitution on the enzyme active site groups occurs and hence is also known as double displacement mechanism. Study of these mechanisms is best approached by rigorous experimental design where data is collected by systematically varying one parameter at a time. This method of reduction is in full display in enzyme kinetics. In fact, elucidating enzyme kinetic mechanisms offers the best example of how scientific hypotheses are tested. Elements of scientific method in sequence include problem recognition → collation of available information → hypothesis building → experimentation → reasoning and deduction → and refining the hypothesis. These steps are iterated in arriving at an enzyme mechanism. Finally when experiments and measurements agree with the theory, truth is secured. In practical enzyme kinetics, this exercise translates into following steps (Table 18.1) for the elucidation of mechanisms.