Reciprocal effects in human hemoglobin: direct measurement of the dimer-tetramer association constant at partial oxygen saturation.

Abstract

An equilibrium gel permeatijn technique was developed for determining as a function of oxygenation state the equilibrium constants for association of Hb subunits. By using this method, the dimer-tetramer constant for human Hb at a partial oxygenation state corresponding to 20% saturation for tetramers was determined as 3.7 .times. 106 M-1 (dimers). Under the same conditions the corresponding constant for fully oxygenated Hb is 4.1 .times. 105 M-1. These results were in good agreement with the predicted behavior of the association reaction based upon oxygen binding curves measured as a function of protein concentration. Thus a high degree of consistency is found between the 2 independent experimental approaches to the reciprocal effects of this linkage system, lending support to the theory proposed earlier for these phenomena.