Final answer:
The trimeric G-protein found in the smooth muscle of blood vessels is the Gq protein, which activates through interactions with the Alpha-1 adrenergic receptor, setting off a chain of reactions leading to muscle contraction and vasoconstriction.
Step-by-step explanation:
The trimeric G-protein identified in the smooth muscle of blood vessels is the Gq protein. It interacts with the Alpha-1 adrenergic receptor and activates phospholipase C (PLC), leading to an increase in inositol triphosphate (IP3) and calcium, which then causes smooth muscle contraction and vasoconstriction. When a signaling molecule binds to a G-protein-coupled receptor in the plasma membrane, a GDP molecule associated with the alpha subunit is exchanged for GTP. The beta and gamma subunits dissociate from the alpha subunit, triggering a cellular response either by the alpha subunit or the dissociated beta-gamma pair. Hydrolysis of GTP to GDP terminates the signal.
Upon the activation of G protein-coupled receptors by ligands, the Gq protein, which consists of alpha (a), beta (β), and gamma (γ) subunits, initiates a signal transduction pathway. This process entails the replacement of guanosine diphosphate (GDP) with guanosine triphosphate (GTP) on the alpha subunit, subsequently activating PLC. The activation of PLC elevates IP3 and calcium levels within the muscle cells, culminating in the contraction of smooth muscles found in various parts of the body such as blood vessels, gastrointestinal system, and more.