title: Simultaneous binding of calcium and vanadate to the Ca2+-ATPase of sarcoplasmic reticulum.
abstract: The interaction of vanadate with the Ca2+-ATPase of sarcoplasmic reticulum vesicles has been studied by making use of the ATPase activity as a measure of uncomplexed enzyme. The binding/dissociation is slow, so that initial rates can be used to study the equilibrium binding. The results indicate that in addition to a Ca2+-free complex E.Van (KV = 0.4 microM), there must also be a Ca2+-enzyme-vanadate complex (K'V = 7 microM). This observation is confirmed by the difference between the kinetics of decay of activity on vanadate addition, and on addition of ATP to enzyme preincubated with vanadate and Ca2+, which requires two enzyme-vanadate complexes. ATP increases the apparent affinity of the enzyme for vanadate by inducing calcium release. Upper limits for the kinetic parameters for vanadate binding and dissociation are estimated.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000252:Calcium-Transporting ATPases / Q000032:analysis / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D014638:Vanadates; D014639:Vanadium / Q000378:metabolism*
chemical_list: D014639:Vanadium; D014638:Vanadates; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium