FIGURE 5.

pH-dependence and correlations with thiol pK_a. A and B, fast reaction between GSH and NO₂-CLA was studied at different pH values using three-component constant ionic strength buffers. Apparent k_onβ (A) and k_offβ (B) values were obtained as in Fig. 1E and Equation 1 from the fit of plots of k_obs 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 k_{on, pH-indep} rate constants (circles, calculated from k_on values at pH 7.4) and k_off (squares) were plotted against thiol pK_a values. Data are from Table 1; a, cysteinylglycine; b, cysteine; c, GSH; d, homocysteine; e, BME.