Table I.
Free radical mechanisms of tyrosine nitration. Rate constants and competing reactions.
| Reaction | Species (R) | k (M−1s−1) | Ref. |
|---|---|---|---|
| One-electron oxidation of tyrosine | |||
| TyrH + R• → Tyr• + RH | CO3•− | 4.5 × 107 | 38 |
| •NO2 | 3 × 105 | 38 | |
| aMe = O | 7.7 × 105 | 6,11 | |
| LOO• | 4.8 × 103 | 11 | |
| LO• | 3.5 × 105 | 21 | |
| •OH | 6.5 × 108 | 11 | |
| Formation of 3-nitrotyrosine | |||
| Tyr• + •NO2 → NO2Tyr | •NO2 | 3 × 109 | 14 |
| •NO | 1 × 109 | 15 | |
| Dimerization and adduct formation | |||
| Tyr• + •R → Tyr adduct | •OHb | 1.2 × 1010 | 11 |
| Tyr• | 2.3 × 108 | 38 | |
| O2•− | 1.5 × 109 | 39 | |
| LOO• | ND | - | |
| GS• | ND | - | |
| Tyrosyl radical reduction | |||
| Tyr• + RH → TyrH + R• | ascorbate | 4.4 × 108 | 18 |
| glutathione | 2 × 106 | 18 | |
a
For MPO compound I. MPO can readily oxidize free tyrosine that can serve as a “shuttle” for secondary oxidation of target protein tyrosines; alternatively, MPO can directly oxidize (expectedly with lower rate constants) protein tyrosines
b
The tyrosyl-hydroxyl radical adduct may evolve to Tyr· via a dehydration reaction (see Fig. 2)
ND, not determined