Polyamine biosynthesis in rat prostate. Substrate and inhibitor properties of 7-deaza analogs of decarboxylated S-adenosylmethionine and 5'-methylthioadenosine

The 7-deaza analogue of 5'-methylthioadenosine, a nucleoside end product in polyamine biosynthesis, has been synthesized. This analogue has been shown to competitively inhibit the hydrolytic cleavage of the purine-ribose bond in methylthioadenosine with Ki congruent to Km. In addition, the 7-deaza analogue of decarboxylated S-adenosylmethionine, a cofactor in the biosynthesis of both spermidine and spermine, has been synthesized. This analogue has been shown to act as a substrate in the reaction catalyzed by spermidine synthase, in which severe substrate inhibition by both the normal nucleoside substrate and the 7-deaza analogue is observed. These results are discussed in terms of possible end product regulation of polyamine biosynthesis and the possible substitution of the nucleoside antibiotic, tubercidin, for adenosine in reactions involving S-adenosylmethionine and its metabolites.