Question #1
Which of the following acts predominatly by activating guanylate cyclase?
With the exception of NO, all of these agents bind to receptors on the cell membrane and activate intracellular signalling cascades.
Receptors for adrenaline, gastrin, sectetin and ACTH are G-protein coupled. Gastrin and secretin exert their effects via the G-protein Gq, which goes on to activate phospholipase C and protein kinase C. ACTH exerts its effects via the G protein Gs, which goes on to activate adenylate cyclase and protein kinase A. Adrenaline activates both Gq and Gs.
ANP directly activates membrane bound guanylate cyclase, with no G protein intermediate. Unlike the other agents listed, NO crosses the cell membrane and activates gualylate cyclase that is dissolved in the cytosol.