Kinetic studies on partially liganded species of carboxyhemoglobin: alpha 2 CO beta 2 and alpha 2 beta 2CO.
The valency hybrids of Hb A, alpha 2CO beta 2+, and alpha 2+ beta 2CO have been prepared by a new high pressure liquid chromatography method, and the kinetics of their CO-combination and dissociation reactions have been studied by double mixing and microperoxidase methods. Both reactions are biphasic. The slow phase in CO-combination and the fast phase in CO-dissociation are due to the reactions of alpha CO2 beta T2 or alpha 2 beta 2CO,T. The fast phase in CO-combination reaction has two components, one due to the dimers of the hybrid and the other due to the R-state tetramer. Immediately after the reduction of the valency hybrids, the overall system is represented by the equation: 2 alpha CO beta in equilibrium alpha 2CO beta 2R in equilibrium alpha 2CO beta 2T or (formula: see text) If the solutions are aged for 3-11 s, the R-state population is reduced gradually to a very small size, and the main species after 11 s of aging are dimers and T-state tetramers. Analysis of the kinetic data indicates slow R in equilibrium T equilibria in the absence of phosphates and significant dissociation of the T-state tetramer. It is concluded that the subunit contacts alpha 1-beta 2 (or alpha 2-beta 1) are impaired seriously in the hybrids. Very slow R in equilibrium T relaxation makes these hybrids unlikely intermediates in the sequential binding of CO to Hb tetramer.
Sharma
V S
VS
Department of Medicine, University of California, San Diego, La Jolla 92093.
D000465:Algorithms; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D004227:Dithionite; D010544:Peroxidases / Q000378:metabolism
D004227:Dithionite; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin; D010544:Peroxidases; C021799:microperoxidase