Interactions entre l'oestradiol et des sites récepteurs utérins

The oestradiol‐binding protein of calf uterine cytosol forms a slowly reversible complex with oestradiol. Kinetic studies on the formation of this complex, carried out with crude or partially purified uterine cytosol preparations, indicate a reaction of the second order. The rate constant shows an inverse relationship with protein concentration. Dissociation of the complex appears to occur in two stages, both following first order reaction rate kinetics. Affinity constants calculated from association‐dissociation kinetics, decrease with increasing temperature. The affinity constant measured under equilibrium conditions shows an inverse relationship with protein concentration, and does not appear to vary at temperatures between 0° and 18°. The treatment of the data from binding studies at equilibrium suggests a cooperative effect. These findings indicate that the interaction between the oestradiol‐binding protein, and its ligand cannot be described by simple reaction schemes; work with purified material, now under progress, could simplify interpretation by eliminating ambiguities due to eventual specific or unspecific protein‐protein interactions in our present impure system.