Kinetics and equilibria of S‐nitrosothiol—thiol exchange between glutathione, cysteine, penicillamines and serum albumin

Publisher Website
Google Scholar
Abstract
The kinetics and equilibria of S‐nitrosothiol‐thiol (SNO—SH) exchange reactions were determined using differential optical absorption. At pH 7.4 and 37°C, k 2 values ranged from 0.9 M−1 · s−1 for the reaction between S‐nitroso‐glutathione (GSNO) and N‐acetyl‐penicillamine, and up to 279 M−1 · s−1 for the exchange between S‐nitroso‐penicillamine (penSNO) and GSH. SNO—SH exchange involving GSH/GSNO and cysteine/cySNO was relatively rapid, k 2 approx. 80 M−1 · s−1 with an equilibrium constant slightly in favour of GSNO. GSNO was strongly favoured in equilibrium with penSNO, k eq 0.0039. In the case of SNO—SH exchange between S‐nitroso human serum albumin (albSNO) and GSH or cysteine k 2 values were 3.2 and 9.1 M−1 · s−1, respectively. The results show that the initial rate of SNO—SH exchange between physiological albSNO (7 μM) and venous plasma levels of GSH and cysteine is very slow, < 1%/min. On the other hand, if a nitrosothiol such as cySNO were to enter a cell, it would be rapidly converted to GSNO (43%/s).