Chain Inequivalence in Bovine Methemoglobin. Progress Report, December 1, 1979-November 30, 1980

摘要

Using pulse-radiolysis, a single-heme in the tetramer of bovine methemoglobin was reduced to the ferro state, producing a valence hybrid (VH). The kinetics of oxygen binding to the VH as well as the re-oxidation of the ferro-heme to the ferric state were studied as a function of pH. The kinetics of the oxygenation revealed the existence of two species, characterized by high and low affinities for oxygen that are associated with two quaternary structures (R and T, respectivey). Above pH 7.7 only the R state could be observed, while below pH 6.5 the T state was dominant. The reaction between the VH and ferricyanide at pH 7.75 (R state) consisted of two equal contributions attributed to the beta and alpha subunits within the tetramer, respectively. At pH 6.3 (T state) a similar phenomenon was observed indicating chain inequivalences both in the T and the R states of methemoglobin. In the presence of inositol hexaphosphate, the T implies R transition was shifted up by about 0.35 pH units. Yet similar rate constants exhibiting similar chain inequivalences have been measured. (ERA citation 05:024733)