Table 1.
Reactivity of cysteines of fully reduced ChTg toward thiol reagents, pH 5.0.
| Reagents | Free Cys | Free GSH | Reduced ChTg | |||
|---|---|---|---|---|---|---|
| k (M−1 s−1) | k (M−1 s−1) | k (M−1 s−1) (-SH/mol ChTg) | E.R. | k (M−1 s−1) (-SH/mol ChTg) | E.R. | |
| GSSG |
0.0028a 0.0008b |
— | 1.1 ± 0.1 (1) |
393 1375 |
0.15 ± 0.03 (6) |
54 187 |
| Cystine | — | 0.048 | 0.56 ± 0.02 (8) | 12 | — | — |
| Cystamine | — | 0.22 | 0.05 ± 0.01 (5) | 0.23 | — | — |
| Homocystine | — | 0.0024 | 0.037 ± 0.003 (6) | 15 | — | — |
| DTNB | — | 20 | 25000 ± 1000 (1) | 1250 | 2300 ± 100 (9) | 115 |
|
DTNB (8 M urea) |
— | 20 |
300 ± 20 (4) 5 ± 1 (6) |
15 0.25 |
— | — |
| CDNB | — | 0.00028 | 0.19 ± 0.01 (10) | 678 | — | — |
|
CDNB (8 M urea) |
— | 0.00028 | 0.0003 | 1 | — | — |
| NBD-Cl | — | 0.032 | 12.6 ± 0.5 (10) | 394 | — | — |
aExperimental value for free cys (pKa = 8.55);
bTheoretical value for unperturbed protein cysteine (pKa = 9.1);
E.R., Enhanced reactivity;
Data are Mean ± S.D.