Negative co-operativity in clustered receptors as a possible basis for membrane action

A model for the interaction of a membrane receptor with a stimulating ligand is presented. It is assumed that (a) the receptor macromolecules are embedded in the membrane as a close packed two-dimensional cluster and (b) strong negative co-operative interaction occurs among the receptor molecules. The model explains the existence of (a) strong membrane stimulation by fractional ligand occupancy of the receptor; (b) the absence of positively co-operative binding curves for ligand to membrane receptors and (c) it provides a molecular explanation for the existence of "spare receptor".