Genes and isozymes.

Abstract

During recent years it has become increasingly apparent that in the cells of a single organism, a number of distinct and separable proteins may exhibit the same or very similar enzyme activities. Such multiple molecular forms of an enzyme are usually referred to as isozymes (or isoenzymes), a term first introduced by Markert & Møller (1959) and now widely found in the biochemical literature. It is a convenient term in practice, because it implies no specific type of structural relationship between the several protein species which may be observed to have similar enzyme activities. Indeed as more and more examples of the phenomenon have been studied, it has become clear that different sorts of molecular relationship are likely to be involved in different cases. About the same time as the widespread occurrence of isozymes was becoming recognized, important advances were also taking place in ideas about the manner in which the genetical constitution of an organism determines the structures of the enzymes that it is capable of synthesizing. The central concept that has emerged is that the primary amino acid sequence of each of the structurally distinct polypeptide chains that occur in the vast array of different enzymes that an organism forms, is encoded in the sequence of base pairs in the DNA of a corresponding gene. The earlier idea expressed by the simple formula one gene-one enzyme , has in effect been superseded as a working hypothesis by the formula one gene-one polypeptide chain .