Regulation of hormone-sensitive adenylate cyclase

Adenylate cyclases in the membranes of eukaryotes are regulated by stimulatory receptors (R_s) and inhibitory receptors (R_i) which activate the catalyst adenylate cyclase (C) through the heterotrimeric GTP-binding proteins, G_s and G_i. The actions of G_s and G_i are not symmetric, since G_s associates tightly with C, whereas G_i does not. Alexander Levitzki analyses the current knowledge and thinking on the mode of interaction between each of these regulatory units and describes one working model which accounts for all the experimental observations and the kinetics involved.