A negative control model of hormone receptor interaction.

An original model of hormone-receptor interaction is proposed: the hormone would interact with its receptor by dissociating a regulatory unit from a catalytic unit, which, freed from the negative constraint exerted by the regulatory unit, would become active. It is shown that such a model shares some features with negatively cooperative models: 1. Scatchard plot has a hyperbolic shape; 2. Dissociation of bound labeled hormone, promoted by chemical dilution is enhanced by an excess of cold hormone. A new graph, in which the ratio between the square of bound hormone concentration and the free hormone concentration is plotted against the bound hormone concentration, allows a discrimination between both models. Moreover, the behavior of a negatively controlled receptor unlike a negatively cooperative one, is critically dependent on its physical state (soluble or particulate). The possible application of this model to hormone responsive adenylate cyclases and other biochemical systems, such as cAMP dependent protein kinases, is mentioned.