The binding of protons and inositol hexakisphosphate to ligated and unligated human des-Arg141alpha-hemoglobin

Van Beek, G.G.; Zuiderweg, E.R.; de Bruin, S.

European Journal of Biochemistry 92(1): 309-316


ISSN/ISBN: 0014-2956
PMID: 32038
Accession: 068518535

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Des-Arg-141.alpha.-Hb was prepared and its proton binding behavior was studied. The difference in protons bound by Hb and des-Arg141.alpha.-Hb apparently cannot be explained by the absence of Arg-141.alpha. Upon removal of Arg-141.alpha., 2 lysyl or arginyl residues apparently became masked and 2 histidyl residues titratable. The Bohr effect of des-Arg141.alpha.-Hb appeared lower than that of Hb. This phenomenon was for the greater part due to the absence of a pK shift of Val-1.alpha. on ligation of des-Arg141.alpha.-Hb. This followed from a study of the pH-dependence of the rate of reaction of 1-fluoro-2,4-dinitro-benzene with the amino group of Val-1.alpha. With inositol hexakisphosphate the Bohr effect of des-Arg141.alpha.-Hb was still smaller than that of Hb with this polyanion. Above pH 7 the proton uptake by des-Arg141.alpha.-Hb on binding of inositol hexakisphosphate was smaller than that observed for Hb. The change in proton binding behavior of Hb on removal of Arg-141.alpha. may have been due to a conformational change in the FG region of the .alpha.-chains. As a result His-89.alpha. became titratable and Lys-90.alpha. or Arg-92.alpha. masked. This change in conformation might also be the reason for the high O2 affinity and the low cooperativity of des-Arg141.alpha.-Hb.