Abstract

Selected nucleosides of adenine and 8-azaadenine were examined as substrates for adenosine kinase (EC 2.7.1.20), an enzyme that catalyzes the phosphorylation of many biologically active nucleosides, to evaluate the effects on substrate activity of various orientations of substituents on the pentofuranosyl ring. The enzyme used was partially purified from cultured H.Ep.2 cells. Although not all the possible isomers were studied, the results, together with other reported findings, lead to the conclusion that necessary, but not sufficient, conditions for substrate activity are the following: (a) the nucleoside should have a 2'-hydroxy group, (b) the 2'-hydroxy group should be trans to the purine moiety, and (c) there should exist a considerable degree of freedom of rotation about the C-1'—N-9 bond. If these conditions are met, the 3'-hydroxy group and the 4'-hydroxymethyl group may be either cis or trans to the purine ring. These results add to understanding of the mode of binding of substrates to adenosine kinase and should aid in the design of new nucleoside analogues as growth-inhibitory on antitumor agents.