pH-dependence and correlations with thiol
pKa.
A and B, fast reaction between
GSH and NO2-CLA was studied at different pH values
using three-component constant ionic strength buffers. Apparent
konβ (A)
and koffβ (B)
values were obtained as in Fig.
1E and Equation 1 from the fit of plots of
kobs
versus GSH concentration to a straight line;
the error bars represent the standard error of
the fit. C and D,
Brønsted plots for fast (C) and slow
(D) reactions. The logarithm of
kon, pH-indep rate constants
(circles, calculated from
kon values at pH 7.4) and
koff (squares)
were plotted against thiol pKa
values. Data are from Table
1; a, cysteinylglycine;
b, cysteine; c, GSH;
d, homocysteine; e,
BME.