Formation and decay of the vanadate complex of the sarcoplasmic reticulum calcium transport protein.
The calcium free sarcoplasmic reticulum calcium transport ATPase incorporates in the presence of magnesium ions approx. 8 nmol monovanadate per mg protein, indicating the formation of a complex containing one vanadate residue per enzyme molecule. On ligand-removal or dilution, the saturated enzyme complex displays biphasic decay kinetics, while the unsaturated complex slowly dissociates monophasically. -Ligand competition by raising the concentrations of unlabeled vanadate results in a progressive decrease of the dissociation rate of the unsaturated enzyme. The complicated dissociation kinetics indicate a sequential mode of interaction between two ligand binding sites. The one to one stoichiometry of the complex suggests that the two sites are located at adjacent ATPase molecules. -It appears unlikely that the decay of the enzyme, vanadate complex is retarded by the formation of a stable quaternary complex between the enzyme, magnesium, mono- and polyvanadate.
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology; D009132:Muscles / Q000201:enzymology / Q000648:ultrastructure; D011817:Rabbits; D011868:Radioisotopes; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D014638:Vanadates; D014639:Vanadium / Q000032:analysis*
D002135:Calcium-Binding Proteins; D011868:Radioisotopes; D014639:Vanadium; D014638:Vanadates; D000251:Adenosine Triphosphatases