title: Reaction cycle of solubilized monomeric Ca2+-ATPase of sarcoplasmic reticulum is the same as that of the membrane form.
abstract: Monomeric Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum dispersed in Triton X-100 is stoichiometrically phosphorylated from Pi in a Ca2+-depleted medium containing dimethyl sulfoxide and catalyzes efficient (80%) phosphoryl transfer to ADP following a jump in water activity in the presence of Ca2+. The Ca2+ concentration dependence of ATP synthesis was sigmoidal (nH = 1.7) and in the millimolar range (K0.5 = 0.3 mM), indicating the involvement of at least two low affinity Ca2+ binding sites. These results, taken together with the properties of the monomer in the forward direction of catalysis, show that the catalytic cycle of the detergent-solubilized monomer is essentially the same as that of the membrane enzyme. The substrate and ion specificity of the catalytic intermediates suggest that the monomer is capable of coupled vectorial transport of Ca2+.
authors.affiliation: Medical Research Council Biomembrane Research Unit, University of Cape Town Medical School, South Africa.
authors.forename: D B
authors.initials: DB
authors.lastname: McIntosh
authors.forename: D C
authors.initials: DC
authors.lastname: Ross
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D003432:Cross-Linking Reagents; D004121:Dimethyl Sulfoxide / Q000494:pharmacology; D008274:Magnesium / Q000494:pharmacology; D009132:Muscles / Q000201:enzymology*; D017830:Octoxynol; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation; D011092:Polyethylene Glycols / Q000494:pharmacology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D012995:Solubility
chemical_list: D003432:Cross-Linking Reagents; D010710:Phosphates; D011092:Polyethylene Glycols; D000244:Adenosine Diphosphate; D017830:Octoxynol; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium; D004121:Dimethyl Sulfoxide