Possible involvement of S-nitrosothiols in the activation of guanylate cyclase by nitroso compounds

Abstract

The inhibitory effects of methemoglobin on activation of coronary arterial soluble guanylate cyclase by nitric oxide (NO), nitroprusside and N-methylN’nitro-N-nitrosoguanidine (MNNG) were described in [ 11. Also dithiothreitol (DTT) enhanced activation of coronary arterial and hepatic soluble guanylate cyclase by nitroprusside and MNNG but not by NO, and reversed the methemoglobin blockade of activation by nitroprusside and MNNG but not by NO. Indeed, DTT was required for hepatic guanylate cyclase activation by nitroprusside. These observations suggested that DTT may react directly with the nitroso compounds to promote release of NO, which may then overcome the inhibition by methemoglobin [ 11. An alternative explanation for the effects of DTT on guanylate cyclase activation was a direct nonenzymatic transfer of the NO-moiety from the nitroso compound to guanylate cyclase (or a ferroheme intermediate) in the presence of thioB. Each of the above hypotheses was tested and the data here illustrate that: (1) Thiols promote release of NO gas from MNNG, but not from nitroprusside, in aqueous neutral buffer. (2) Inhibition of guanylate cyclase activation by NO varies directly with the concentration of methemoglobin and indirectly with the amount of NO. (3) Thiols react with NO to form stable S-nitrosothiols which are potent activators of guanylate cyclase .