Abstract
Abstract The human hemoglobin (Hb) mutant Chesapeake (α92 Arg→Leu) is characterized by increased oxygen affinity, a Bohr effect, and a lowered value of n in Hill's equation in the midrange of saturation. The data presented here demonstrate that, in addition, the dissociation of oxygen from oxy Hb Chesapeake proceeds with a rate of 15 per s and that the carbon monoxide binding proceeds with a slightly accelerating time course at a rate of 3.5 x 105 m-1 s-1. The reactions of bromthymol blue and p-hydroxymercuribenzoate with oxy and deoxy Hb Chesapeake demonstrate that the R ⇄ T interconversion does occur in this mutant. Finally, oxygen binding and the oxygen equilibrium curve can be satisfactorily accounted for by a Monod, Wyman, Changeaux model (in its simplest form) with a small value of L (5 to 10) and a normal value of c. These results are in agreement with the analysis of Edelstein (Edelstein, S. (1971) Nature 230, 224–227) and the predictions of Shulman et al. (Shulman, R. G., Ogawa, S., and Hopfield, J. J. (1972) Arch. Biochem. Biophys. 151, 68–74) that the functional properties of Hb Chesapeake can be explained by an early conversion from the T to the R state as ligand binding progresses.
Published Version
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