Cooperative effects in hemoglobin and allosteric enzymes

Cooperative effects in the binding of oxygen to hemoglobin have been known and studied for some time. The degree of cooperativity is reflected in the S or sigmoid saturation curve (i.e. percentage of oxygenated hemoglobin as a function of the partial pressure of oxygen) showing that the binding of a few oxygen molecules favours the binding of more and that binding occurs best at high oxygen concentrations.