Beta-adrenergic receptors mediate the catecholamine-induced activation of adenylate cyclase through the action of G proteins. The beta-2-adrenergic receptor binds epinephrine with an approximately 30-fold greater affinity than it does norepinephrine (By similarity). Highly expressed in the liver and red and white muscle, with lower levels of expression in the gills, heart, kidney and spleen. Lacks the regulatory protein kinase A phosphorylation sites within the G-protein binding domain that mediate desensitization and are present in mammalian homologs. Belongs to the G-protein coupled receptor 1 family. Adrenergic receptor subfamily. ADRB2 sub-subfamily.