On the Evolution of Biochemical Syntheses

Although it has been recognized for a long time that the biochemistry of the organism is conditioned by its genetic constitution, a more precise definition of this dependence has not been possible until recently. A considerable amount of evidence now exists for the view that there is a one-to-one correspondence between genes and biochemical reactions. This concept, foreshadowed in the work of Garrod(1) on human alcaptonuria, accounts in a satisfactory way for the inheritance of pigment formation in guinea pigs,(2) insects(3) and flowers,(4) and the synthesis of essential growth factors in Neurospora.(5) It appears from these studies that each synthesis is controlled by a set of non-allelic genes, each gene governing a different step in the synthesis. As to the nature of this control, it is probable that the primary action of the gene is concerned with enzyme production. That genes can direct the specificities of proteins has been shown in the case of many antigens,(6) while several mutations demonstrably affecting the production of enzymes have been reported.(6) Evidence on the postulated gene-enzyme relationship is in most cases, however, still circumstantial; this is partly because of technical difficulties involved in the study of synthetic, or free-energy consuming reactions in vitro, and partly because of the insufficiency of biochemical information on those reactions which happen to be susceptible of genetic analysis.