Table 1.
Reaction rates of cobinamide (Cbi), cobalamin, imisopasem, and MnTBAP with reactive oxygen and nitrogen species.
| Compound | Superoxide (O2·−)(a) | Hydrogen peroxide (H2O2)(b) | Peroxynitrite (ONOO−) | Nitric oxide (·NO) |
|---|---|---|---|---|
| Cbi(III) | 1.1 × 108 (c) | 8.0 × 102 (c) | Not studied | 2.4 × 108 (51) |
| Cbi(II) | 1.9 × 108 (c) | 3.7 × 104 (c) | 6.3 × 106 (c) | Ka: 1.3 × 1010 (51) |
| Cobalamin(III) | 9.4 × 106 (c) | 4.5 × 106 (17) | ( d ) | No activity (51,71) |
| Cobalamin(II) | 3.8 × 108 (13) | 1.4 × 102 (16) | 3.7 × 105 (14) | Ka: 1.5 × 108 (51) |
| Imisopasem | 1.6 × 107 (24) | 8.2 (25) | No activity (26) | No activity (26) |
| MnTBAP | ∼ 4.0 (54) | 5.8 (25) | ∼ 1 × 105 (27) | No activity (28) |
Reactions of the indicated compounds with O2·−, ONOO−, and ·NO are all second order reactions with rate constants in units of M−1 s−1. The reactions of Cbi(III) and Cbi(II) with H2O2 are third order with rate constant units of M−2 s−1. Cbi(II) and cobalamin(II) bind nitric oxide, so a Ka is shown in units of M−1. For the new data presented in this study, rate constants were measured for O2·− using a hypoxanthine–xanthine oxidase-cytochrome c system, for H2O2 using a H2O2-specific sensor (World Precision Instruments), and for ONOO− using a stopped-flow instrument. Published rate constants for Cu/Zn and Mn SODs and catalase are shown for reference.a, b Letters and numbers in parenthesis refer to footnotes and references, respectively.
Mammalian catalase: 1.5 × 106 (25).
New data presented in this study.
No published data found.