Mechanism of activation of soluble guanylate cyclase by guanidine thiols--a new class of enzyme activators.

The study is concerned with the mechanism of activation of soluble guanylate cycla-se by guanidine thiol derivatives-a new class of enzyme activators. Guanidine thiols contain both the guanidine and SH group which act, respectively, as donor and acceptor of nitric oxide (NO). The role of guanidine thiol SH group in the mechanism of soluble guanylate cyclase activation was studied. Three guanidine thiol derivatives were tested: mercaptoethylguanidine, its disulfide and S-methyl mercaptoethylguani-dine. All three compounds proved to be NO-synthase substrates and, simultaneously, guanylate cyclase activators. The degrees of guanylate cyclase activation by mercaptoethylguanidine and its disulfide were, respectively, two and four times higher than that by L-arginine. The stimulatory effects of S-methyl mercaptoethylguanidine and L-arginine were evaluated and found to be of the same order. The important role of S-acceptor group of guanidine thiols in the mechanism of guanylate cyclase activation increase provides an explanation for different intensities of guanylate cyclase activation by the compounds tested. NO-acceptor properties of guanidine thiols disulfide bonds in the synthase mechanism of NO generation were first reported.