Gdp

figure 11-14 Adrenergic receptor activation-inactivation. Agonist binding to the /32-adrenergic receptor initiates two concurrent processes, one of which results in effector activation, while the other activates pathways that modulate receptor function and result in receptor desensitization. One important mechanism of desensitiza-tion is effected by a receptor-specific kinase (i.e., /3ARK) that phos-phorylates the /32-adrenergic receptor and causes uncoupling from the G protein. Abbreviations: jSARK, /3-adrenergic receptor kinase; AC, adenylyl cyclase; EPI, epinephrine; ccs, /3, y, G-protein subunits. Reproduced from Lomasney, J. W., Allen, L. F., and Lefkowitz, R. J. (1995). Cloning and regulation of catecholamine receptor genes. In "Molecular Endocrinology" (B. D., Weintraub, ed.), pp. 115-131. Raven Press, New York.

figure 11-13 Outline of the function of an a2-receptor for epinephrine. The hormone interacts with the a2-receptor in the cell membrane and exerts inhibition of adenylate cyclase activity. This requires the binding of GTP to the guanine nucleotide-transducing agent Gj, whose concerted action with the ligand receptor results in the inhibition of the enzymatic reaction.

these several individual enkephalins of the adrenal medulla, contains one Leu- and six Met-enkephalin sequences. The structure of human adrenal proenkephalin mRNA and protein is shown in Figure 11-15. This

Gs protein i

figure 11-13 Outline of the function of an a2-receptor for epinephrine. The hormone interacts with the a2-receptor in the cell membrane and exerts inhibition of adenylate cyclase activity. This requires the binding of GTP to the guanine nucleotide-transducing agent Gj, whose concerted action with the ligand receptor results in the inhibition of the enzymatic reaction.

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