The second-messenger system for non-steroid hormones involves the hormone binding to a cell receptor, activating adenylate cyclase, and producing cyclic AMP, which triggers a cascade of cellular activities. Alternatively, calcium ions may act as a second messenger following activation of phospholipase C.
Steps of the Second-Messenger System
The second-messenger system is a mechanism of action for non-steroid hormones. Initially, the hormone binds to a receptor on the cell membrane. Following this, the receptor undergoes a conformational change and activates an enzyme, usually adenylate cyclase. This enzyme then converts ATP to the second messenger cyclic AMP (cAMP). cAMP functions to activate protein kinases, which then promote a phosphorylation cascade, impacting various proteins and cellular functions.
Calcium ions can also serve as a second messenger in an alternative pathway. Here, G proteins activate phospholipase C (PLC), leading to the production of diacylglycerol (DAG) and inositol triphosphate (IP3). IP3 mobilizes calcium ions from intracellular stores, and along with DAG, activates protein kinases for further signal transduction.