title: Influence of the 53 kDa glycoprotein on the cooperativity of the Ca(2+)-ATPase of the sarcoplasmic reticulum.
abstract: Previous results from this laboratory suggest that the 53 kDa glycoprotein (GP-53) of rabbit skeletal muscle sarcoplasmic reticulum membrane (SR) may influence coupling between Ca2+ transport and ATP hydrolysis by the Ca(2+)-ATPase. Here we report evidence that GP-53 may influence the cooperative behavior of the Ca(2+)-ATPase. The ATPase activity of the Ca(2+)-ATPase displays negative cooperative dependence (Hill coefficient n less than 1) on [MgATP] and has positive cooperative dependence (n greater than 1) on [Ca2+]free. We have determined the degree of cooperativity for native SR vesicles, SR preincubated with antiserum against GP-53 or preimmune serum, and SR partially extracted with KCl-cholate. Our results show that SR preincubated with preimmune serum or SR treated with cholate in 50 mM KCl (yielding membranes rich in GP-53) demonstrate a cooperative dependence of Ca(2+)-ATPase activity on both [ATP] and [Ca2+] similar to that of untreated SR. SR preincubated with anti-GP-53 antiserum (which causes an uncoupling of Ca2+ transport from ATP hydrolysis) or SR extracted with cholate in 1 M KCl (yielding membranes depleted of GP-53) displays decreased positive cooperative dependence on [Ca2+] and decreased negative cooperative dependence on [ATP]. The results are consistent with the interpretation that GP-53 may influence the cooperative behavior of the Ca(2+)-ATPase.
authors.affiliation: Department of Physiology, University of Virginia, Charlottesville.
authors.forename: H
authors.initials: H
authors.lastname: Kutchai
authors.forename: K
authors.initials: K
authors.lastname: Boyd
authors.forename: Q
authors.initials: Q
authors.lastname: Xu
authors.forename: C P
authors.initials: CP
authors.lastname: Weis
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D019826:Cholic Acid; D002793:Cholic Acids; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009132:Muscles / Q000201:enzymology; D011189:Potassium Chloride; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D002793:Cholic Acids; D008562:Membrane Glycoproteins; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D019826:Cholic Acid; D002118:Calcium