Inhibition Analysis and Inhibitor-resistant Enzymes

Journal/Book: Reprinted from Nature Vol. 198 No. 4884 pp. 992-993 June 8 1963. 1963;

Abstract: Department of Chemistry Arizona State University Tempe. AMINO-ACID analogues have proved very useful in numerous investigations involving micro-organisms1. Among these applications is the technique of inhibition analysis whereby one makes a structural comparison of related molecules that competitively inhibit the growth of micro-organisms in order to derive information about the nature of an enzyme-substrate complex2. Thus the conclusion has been reached that the - and -carbons must lie in a trans-like conformation when lysine is complexed to the enzyme surface3. The terminal and -methylene groups of methionine were reported to be cis-like to each other in the enzyme-substrate complex4. The steric and spatial relationships of the ring carbons to the -carbon position of the alanine side-chain of certain analogues seemingly dotermine whether the phenylalanine or the leucine enzyme-substrate complex mimicked5. This approach avoids the necessity of actually isolating the enzyme in question but it does not completely allay the doubts that more than one enzyme in the intact organism is being inhibited by the selection of antagonists used. It seems probable that the several enzymes involving any specific amino-acid as substrate could show differential inhibition patterns because they complex in varying manners with the natural amino-acid substrate. In particular an inhibition analysis with amino-acids such as leucine phenylalanine and lysine is susceptible to error. These compounds have shown very little specialized function which could be metabolically isolated from their primary role of general protein synthesis. Harding and Shive6 suggested that cyclopentanoglycine may inhibit a relatively few of the functions of isoleucine but the evidence was incomplete. Martins has pointed out the necessity for amino-acid analogues to show differential antimetabolite action and indicated that a low concentration of ethionine could preferentially prevent the conversion of methionine to cystine without exerting a direct effect an protein formation. However it would seem that an inhibition analysis investigation with methionine analogues would have a greater chance of success due to the possibility of selectively inhibiting the methyl-transfer function. ... ___MH

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