Are thiols the carrier of nitric oxide in biological systems? A kinetic model

The generation and decomposition of nitrosothiols formed in a reaction of nitric oxide with cysteine and other thiols was investigated. The thiols selected had various steric, electronic, and other structural properties that affected the stability of the nitrosothiols derived from them. Rates of these reactions were measured over the range from 17 to 37 degrees C. The production of nitrosothiols in aerobic acid solutions is very rapid. However, the release of nitric oxide is a zero-order reaction with extremely low rate constants-k(0) = 4.55 x 10(-8) (mol/L) s(-1) at 37 degrees C in a 1.46 x 10(-4) mol/L nitroso-glutathione solution at pH 7.4. The rate constant k(0) depends on the initial concentration, indicating that one of the products participates in the reaction. Favorable tertiary structure for disulfide formation or electronic interactions in the nitrosothiol molecule accelerate the release of nitric oxide. It is possible that these processes trigger, at least partially, the NO release in biological systems. (C) 1997 Academic Press.