<prompt> When activated by b-adrenergic receptors, the G protein:Activates phospholipase CActivates adenylate cyclaseActivates protein kinase CConves guanosine diphosphate GDP to guanosine triphosphate GTP  <response>: When norepinephrine binds to a beta-adrenergic receptor, it activates a G protein i.e., a guanosine triphosphate GTP binding protein, which, in turn, activates adenylate cyclase. Adenylate cyclase catalyzes the formation of cyclic adenosine 3,5-monophosphate cAMP, which activates a variety of kinases. One of these kinases protein kinase A phosphorylates phospholamban, which reduces the inhibition of the sarcoplasmic reticular Ca2 pump, increasing sequestration of Ca2 from the cytoplasm. Ref: Biaggioni I., Robeson D. 2012. Chapter 9. Adrenoceptor Agonists Sympathomimetic Drugs. In B.G. Katzung, S.B. Masters, A.J. Trevor Eds,Basic Clinical Pharmacology, 12e. 