The reaction between organic nitrates and sulfhydryl compounds. A possible model system for the activation of organic...

The rate of loss of the sulfhydryl group, determined with the Ellman reagent, was used to derive second order rate constants for the reaction of a series of organic nitrates with a series of sulfhydryl compounds. For the organic nitrates, increases in the rate of reaction with cysteine, in general, ran parallel both with increases in pharmacological potency (flow in the Langendorff heart) and with increases in total clearance. Cysteine was the most active sulfhydryl compound examined, which is compatible with a possible role as an important nitrate receptor. Under some conditions the rate of loss of the sulfhydryl group was much greater than the rate of formation of nitrite ion. This indicates the presence of a reaction intermediate, probably a thionitrate. It is suggested that, in vivo, a thionitrate could function as an important intermediate in the activation of guanylate cyclase.