Dimer-monomer dissociation of human hemoglobin A

• Published in: The Journal of biological chemistry Vol. 259; no. 23; pp. 14544 - 14547
• Main Authors: Shaeffer, J R, McDonald, M J, Turci, S M, Dinda, D M, Bunn, H F
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 10-12-1984; American Society for Biochemistry and Molecular Biology
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Carboxyhemoglobin - metabolism; Fundamental and applied biological sciences. Psychology; Globins - isolation & purification; Hemoglobin A - metabolism; Hemoproteins; Humans; Kinetics; Macromolecular Substances; Mathematics; Metalloproteins; Proteins; Tritium; Human; Hemoglobin A; Hemoprotein; Radiolabelling; Alpha-Peptide chain; Dimer; Monomer; Molecular dissociation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(17)42634-2

Isolated 3H-labeled human hemoglobin alpha chains were incubated with unlabeled carbonmonoxyhemoglobin A for 72 h in 0.01 M potassium phosphate, pH 7.0, at 25 degrees C. Following separation of the free alpha chain monomers and Hb A (alpha 2 beta 2) tetramers by electrophoresis on cellulose acetate strips or by chromatography on DEAE-cellulose columns, analysis of radioactivity showed a slow transfer of 3H-labeled alpha chains into Hb A. Separation of the globin chains of the isolated [3H] Hb A on a CM-cellulose column in 8 M urea showed that the radioactivity was in structurally intact alpha chains. Gel filtration of a reaction mixture on Sephadex G-75 in the presence of 0.15 M NaCl showed that the 3H-labeled alpha-chains in Hb A were an integral part of, and not nonspecifically adsorbed to, the tetramer. These results indicate that the free 3H-labeled alpha chain monomers were incorporated into Hb A by exchange with pre-existing unlabeled alpha chain subunits according to the scheme, alpha 2 beta 2 in equilibrium 2 alpha beta in equilibrium 2 alpha + 2 beta. The rate constant for the dissociation of alpha beta dimers to alpha and beta monomers, the rate-limiting step in this exchange reaction, was 4.0 (+/- 0.7) X 10(-3) h-1.