Mode of coupling between hormone receptors and adenylate cyclase elucidated by modulation of membrane fluidity [14]

THE hormone- and neurotransmitter-dependent adenylate cyclases represent transmembrane regulatory systems in which the receptor unit faces the outside of the cell and the cyclase catalytic unit faces the inside. When the hormone or neurotransmitter binds to the receptor, the catalytic unit of the cyclase is activated and produces cyclic AMP at the inner surface of the membrane ¹. It has recently become clear that some hormone receptors are permanently coupled to adenylate cyclase whereas others are not. We demonstrate here that the effects of modulating membrane fluidity on the rate of adenlyate cyclase activation can be used to distinguish between the two modes of coupling.