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.