<prompt> All are second messengers exceptGuanylyl cyclasecAMPIP3DAG  <response>: Ans. a Guanylyl cyclaseRef: Ganong, 25th edp.56The second messenger systems that are activated through coupling of hormone-receptor complexes by G-protein are,Adenylyl cyclase-cAMP systemInositol triphosphate IP3 - Diacylglycerol DAG - Calcium Ca2 systemGuanylyl cyclase-cGMP systemGuanylyl cyclase is the enzyme responsible for formation of nitric oxide. Nitric oxide is the second messenger involved in cell signaling 