Zavodnik I B, Piletskaia T P, Stepuro I I
Mol Biol (Mosk). 1992 Mar-Apr;26(2):321-7.
The processes of reversible oxygen binding and nonreversible autoxidation of human hemoglobin were studied. The activation energy of the oxygen binding, as determined by the temperature dependence of the P50 parameter, was 26 +/- 4 kJ/mol, the activation energy of the autoxidation, as determined by the temperature dependence of the apparent rate constant of autoxidation, was 120 +/- 15 kJ/mol. Pyridoxal phosphate decreased the oxygen affinity of hemoglobin, slightly diminished the cooperativity of the oxygenation process and unaffected the activation energy of the oxygen binding. Pyridoxal phosphate slightly reduced the Bohr coefficient value from 0.70 to 0.65. Pyridoxal phosphate, but not pyridoxal, raised the apparent rate constant of autoxidation reaction. The rate of autoxidation significantly increased as the pH value of the medium decreased, reflecting, probably, protonation of the distal histidine of the hemoglobin. The activation energy of autoxidation was independent of pH. Aliphatic alcohols also increased the rate of the autoxidation process, probably, either by stabilization of the hemoglobin T-state, or by direct nucleophilic displacement of the oxygen molecule.
对人血红蛋白的可逆氧结合和不可逆自氧化过程进行了研究。通过P50参数的温度依赖性确定的氧结合活化能为26±4 kJ/mol，通过自氧化表观速率常数的温度依赖性确定的自氧化活化能为120±15 kJ/mol。磷酸吡哆醛降低了血红蛋白的氧亲和力，略微降低了氧合过程的协同性，且不影响氧结合的活化能。磷酸吡哆醛使玻尔系数值从0.70略微降低至0.65。磷酸吡哆醛而非吡哆醛提高了自氧化反应的表观速率常数。随着介质pH值降低，自氧化速率显著增加，这可能反映了血红蛋白远端组氨酸的质子化。自氧化的活化能与pH无关。脂肪醇也提高了自氧化过程的速率，这可能是通过稳定血红蛋白的T态，或通过直接亲核取代氧分子来实现的。
