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 p roperties that affected the stability of the nitrosothiols derived fro m them. Rates of these reactions were measured over the range from 17 to 37 degrees C. The production of nitrosothiols in aerobic acid solut ions is very rapid. However, the release of nitric oxide is a zero-ord er reaction with extremely low rate constants-k(0) = 4.55 x 10(-8) (mo l/L) s(-1) at 37 degrees C in a 1.46 x 10(-4) mol/L nitroso-glutathion e solution at pH 7.4. The rate constant k(0) depends on the initial co ncentration, indicating that one of the products participates in the r eaction. Favorable tertiary structure for disulfide formation or elect ronic interactions in the nitrosothiol molecule accelerate the release of nitric oxide. It is possible that these processes trigger, at leas t partially, the NO release in biological systems. (C) 1997 Academic P ress.