Stereochemistry of Cooperative Effects in Hemoglobin

stereochemical interpretation of the cooperative effects in hemoglobin. Here we wish to outline the main features of this mechanism and to describe experiments performed to test certain of its aspects. The oxygen affinity of hemoglobin depends on the number of oxygen molecules combined, on pH and on the concentration of 2,3-diphosphoglycerate (2,3-DPG). These cooperative ffects arise from a reversible transition between two forms which differ in tertiary and quaternary structure. One of these, the deoxy form, is normally restricted to the five-coordinated ferrous tate. The oxy form is usually found whenever the iron is six-coordinated, regardless of the nature of the ligand and the valency or spin state of the iron atom. The only