Hemoglobin Chesapeake (92α, Arginine → Leucine): PRECISE MEASUREMENTS AND ANALYSES OF OXYGEN EQUILIBRIUM

Abstract

Abstract Precise oxygen equilibrium curves of hemoglobin (Hb) Chesapeake and human adult hemoglobin (Hb A) were determined by the automatic recording method in the presence and absence of NaCl, 2,3-diphosphoglycerate (DPG), and inositol hexaphosphate (IHP). The Adair constants, k1, k2, k3, and k4, and some oxygenation parameters were obtained from the equilibrium data. Maximum slope of the Hill plot for Hb Chesapeake, which was 1.22 under stripped conditions, was profoundly increased on the addition of 2 mm DPG and still more, beyond 2, on the addition of 2 mm IHP. It has been shown that DPG increases the cooperativity of oxygen binding to Hb Chesapeake by reducing k1, k2, and k3 without significant change of k4, as previously observed in Hb A. Within experimental errors, the k4 value for Hb Chesapeake was equal to that for Hb A whether DPG was present or absent. The ki value for Hb Chesapeake did not monotonously increase with i: k3 was significantly smaller than k2 whether DPG and IHP were present or absent. This resulted in slightly biphasic oxygen equilibrium curves of Hb Chesapeake. The biphasic oxygen binding was tentatively interpreted as a result of significantly cooperative interactions between the α1 and β1 (and α2 and β2) subunits and impaired subunit interactions at the α1β2 (and α2-β1) interface.