へムたんぱく-ガス状リガンド結合の反応速度論 ： Ⅱ. グリコシル化微少ヘモグロビン，Hb Aɪс，Aɪь，Aɪa₂，Aɪa₁，およびHb Hope，β136(H 14)Gly→Asp，について

Abstract

The kinetics of the ligand binding to the glycosylated minor components of human adult hemoglobin (Hb Aɪс Aɪь, Aɪa₂ and Aɪa₁) and a variant hemoglobin, Hb Hope, were studied with the stopped-flow method. The rate constants of O₂ dissociation and CO association for the minor hemoglobins were less affected by 2, 3-diphosphoglycerate (DPG) or inositol hexaphosphate (IHP) than for the major component, Hb A₀. The rate constants for Hb Aɪa₁ and Aɪa₂ were practically unaffected by these organic phosphates. As for Hb Hope, the effects of DPG and IHP were reduced on the CO association rate constant (l'), but not on the O₂ dissociation rate constant (k). These results were consistent with the O₂ equilibrium findings. Hb Aɪa₁ and Aɪa₂, and Hb Hope exhibited biphasic O₂ dissociation kinetic profiles. The rate constants for the slow phase were in good agreement with that of O₂ dissociation from the isolated α chain of normal human adult hemoglobin (Hb A₀). The rate constant of O₂ dissociation from the isolated β chain of Hb Hope was approximately 4 times larger than that from the β chain of Hb A₀. It is highly probable that the biphasic O₂ dissociation kinetics reflect the large difference in reactivity to the ligand between α and β chains. I discuss the structure-function relationship of these β-variant hemoglobins from a kinetic standpoint.