The effect of pH on the rate of dissociation of the oxygenated beta chain tetramer of Hb A

• Published in: Biochemical and biophysical research communications Vol. 111; no. 1; pp. 55 - 60
• Main Authors: Turci, Susan M., McDonald, Melisenda J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 28.02.1983
• Subjects: Hemoglobin A - metabolism; Hydrogen-Ion Concentration; Kinetics; Macromolecular Substances; oxyhemoglobin A; Oxyhemoglobins - metabolism; Time Factors
• ISSN: 0006-291X; 1090-2104
• DOI: 10.1016/S0006-291X(83)80116-8

The effect of pH on the overall assembly of oxyhemoglobin A following mixing of equivalent concentrations of α and β heme subunits has been studied in 0.1 M potassium phosphate buffers at 20°C. The resultant kinetic profiles monitored at 582.5 nm (the maximum of the oxyhemoglobin — oxy chain difference spectrum) were homogeneous and appeared to be first order. The rate of these exponential time courses, reflecting the rate of dissociation of the β chain tetramer, increased from 0.013 min −1 at pH 6.4 to 0.30 min −1 at pH 8.0 and 1.0 min −1 at pH 8.5. Concurrent with this increased rate was a decrease in the overall color yield from the reaction. The absorbance changes, which involve a significant contribution from the β chain tetramer to monomer dissociation step, changed three fold over the pH range studied. The findings indicate that protons enhance the stability of the β chain tetramer.