title: Cyclic adenosine monophosphate dependent and independent phosphorylation of sarcolemma membrane proteins in perfused rat heart.
abstract: This study was initiated in order to elaborate further on the mechanism by which epinephrine modulates cardiac function via protein phosphorylation. A membrane fraction has been isolated from freeze-clamped perfused rat heart that contains two phosphoproteins. These proteins have molecular weights of 36,000 (A protein) and 27,000 (B protein). The phosphorylation of the A protein occurs during the equilibration of the heart with inorganic [32P]phosphate. The phosphorylation of the B protein occurs in response to epinephrine. The A and B proteins are apparently identical with two phosphoproteins in enriched preparations of sarcolemma. The protein of the sarcolemma preparation equivalent to the A protein is phosphorylated in vitro by both cAMP-independent and cAMP-dependent protein kinases. The phosphorylation of the protein of the sarcolemma preparation equivalent to the B protein is catalyzed by the cAMP-dependent protein kinase. Thus the patterns of phosphorylation of these proteins in vivo and in vitro are compatible. The phosphorylation of the B protein has been documented in vitro to modulate calcium transport (Will, H., et al. (1973) Acta Biol. Med. Ger. 31, 45-52), but the response to epinephrine in the perfused heart is not apparently coordinated with the catecholamine-induced inotropic effect.
mesh_terms: D000818:Animals; D002458:Cell Fractionation / Q000379:methods; D000242:Cyclic AMP / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D008970:Molecular Weight; D009206:Myocardium / Q000201:enzymology / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D051381:Rats; D012508:Sarcolemma / Q000378:metabolism
chemical_list: D008565:Membrane Proteins; D010750:Phosphoproteins; D000242:Cyclic AMP; D011494:Protein Kinases; D004837:Epinephrine