High efficiency Ca2+ transport by the sarcoplasmic reticulum Ca2(+)-ATPase in the absence of the 53-kilodalton glycoprotein.
Although the Ca2(+)-ATPase is the predominant protein species of the skeletal sarcoplasmic reticulum membrane, the functional significance of other minor protein species remains unresolved. The proposition has been tested that the membrane-bound 53-kDa glycoprotein (GP-53) may be required or significantly involved in regulating the coupling of ATP hydrolysis to Ca2+ transport by the Ca2(+)-ATPase. Ca2(+)-ATPases originating from preparations with and without GP-53 were reconstituted into phosphatidylcholine liposomes, and Ca2+ uptake and pumping efficiency were determined. The reconstituted Ca2+ pump from all preparations transported Ca2+ with high efficiency (Ca2+:ATP greater than 1.5). The results demonstrate that GP-53 is not required to couple ATP hydrolysis to Ca2+ transport. Additionally, the observed high coupling efficiency is inconsistent with GP-53 functioning as a substantial positive regulator of coupling.
Martin
D W
DW
Department of Medicine, State University of New York, Stony Brook 11794.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000302:isolation & purification / Q000378:metabolism*; D006023:Glycoproteins / Q000378:metabolism; D007700:Kinetics; D008081:Liposomes / Q000378:metabolism; D008970:Molecular Weight; D009132:Muscles / Q000378:metabolism; D011510:Proteolipids / Q000378:metabolism; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D006023:Glycoproteins; D008081:Liposomes; D011510:Proteolipids; C020485:proteoliposomes; D000001:Calcimycin; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium