88 The Nature of Biological Diversity 



In one instance, ATP cleavage may induce structural change; in the 

 other, structural change may induce ATP formation. 



Past experience suggests that further work will likely show the 

 last speculation to he invalid, hut the possibility that such apparently 

 diverse processes as oxidative phosphorylation and muscle contraction 

 may have an important, common mechanistic feature is indeed an in- 

 triguing one. 



Genetic control of and induced change 

 in the nature of enzymes 



A lecture under the heading of the nature and diversity of catalytic 

 proteins would not he complete without some consideration of the 

 factors governing the formation of enzymes. Two exciting areas of 

 research are on the genetic control of the fine structure of enzymes 

 and on the nature of enzymic changes which lead to resistance to 

 antihiotics and anticancer agents. 



As an example of genetic control of the fine structure of an enzyme, 

 the excellent researches of Hotchkiss and Evans (40) may he cited. 

 Concepts which have arisen from their work on the genetic modifica- 

 tion of a pneumococcal enzyme involved in folic acid synthesis from 

 p-aminobenzoic acid, are shown schematically in Fig. 9. Most of the 

 studies of gene-enzyme relationships have concerned all-or-none 

 effects — either a particular enzyme is present or is absent in a given 

 genetic strain. Hotchkiss and Evans have obtained strong genetic 

 evidence that the difference in relative affinities for various analogs of 

 p-aminobenzoate noted in their studies results from the variations in 

 the fine structure of a single enzyme. They suggest, as noted in 

 Fig. 9, that DNA controls not only the presence of the enzyme, but 

 that variation in the fine structure of the DNA can result in variation 

 in the enzyme as reflected by the change in inhibitory effects of 

 chemical modifications of p-aminobenzoate. As noted by these ob- 

 servers, there will remain some doubt about the interpretation 

 until purification of the enzymes involved can be achieved, but the 

 way seems clear and the authors appropriately state, "It would be a 

 challenging prospect to learn about the linear sequence of amino 

 acids in a series of proteins which have such interesting and charac- 

 teristic properties in their native folded forms." 



Problems of keen fundamental as well as practical importance 

 arise from consideration of the factors responsible for the develop- 



