Autooxidation and oxygenation of human hemoglobin
Zavodnik, I.B.; Piletskaia, T.P.; Stepuro, I.I.
Molekuliarnaia Biologiia 26(2): 321-327
1992
ISSN/ISBN: 0026-8984 PMID: 1339953 Document Number: 395395
The processes of reversible oxygen binding and nonreversible autoxidation of human hemoglobin were studied. The activation of energy of the oxyen 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.