title: Interaction of valinomycin and monovalent cations with the (Ca2+,Mg2+)-ATPase of skeletal muscle sarcoplasmic reticulum.
abstract: The interactions of monovalent cations and of the K+-specific ionophore, valinomycin, with the Ca2+-ATPase of skeletal muscle of sarcoplasmic reticulum have been studied in the absence of cation gradients by their effects on enzyme turnover and on the ATP plus Ca2+-dependent enhanced fluorescence of the ATP analogue, 2',3'-O-(2,4,6-trinitrocyclohexyldienylidine)-adenosine 5'-triphosphate (TNP-ATP) (Watanabe, T., and Inesi, G. (1982) J. Biol. Chem. 257, 11510-11516). Monovalent cations decreased turnover-dependent TNP-ATP fluorescence in the series K+ greater than Rb+ approximately equal to Cs+ greater than Na+ greater than Li+ (K0.5 = 49, 73, 75, 94, and 246 mM, respectively), consistent with the known specificity of the monovalent cation binding site that stimulates turnover and E-P hydrolysis. Valinomycin (200 nmol/mg), in the absence of monovalent cations, decreased ATPase activity by 30% and abolished the stimulatory effects of 150 mM KCl or NaCl on turnover. The ionophore alone enhanced TNP-ATP fluorescence by 20% and altered the specificity and affinity of the site that inhibited TNP-ATP fluorescence to Cs+ greater than Rb+ greater than K+ approximately equal to Na+ greater than Li+ (K0.5 = 79, 111, 134, 136, and 270 mM, respectively), which follows the Hofmeister series for effectiveness of monovalent lyotropic cations. TNP-ATP binding was not affected by either monovalent cations or valinomycin. Inhibition of turnover-dependent TNP-ATP fluorescence appears to be a useful parameter for monitoring monovalent cation binding to the Ca2+-ATPase. It is concluded that the ionophore interacts directly with the Ca2+-ATPase, independent of its K+ conductance effects on the lipid bilayer, and modifies the affinity and specificity of the monovalent cation site, either by direct interaction or by the formation of a valinomycin-monovalent cation-enzyme complex.
authors.forename: G A
authors.initials: GA
authors.lastname: Davidson
authors.forename: M C
authors.initials: MC
authors.lastname: Berman
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002414:Cations, Monovalent; D007700:Kinetics; D009132:Muscles / Q000201:enzymology; D011189:Potassium Chloride / Q000494:pharmacology; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D012965:Sodium Chloride / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D014634:Valinomycin / Q000494:pharmacology*
chemical_list: D002414:Cations, Monovalent; D014634:Valinomycin; D012965:Sodium Chloride; C045674:2',3'-O-(2,4,6-trinitro-cyclohexadienylidine)adenosine 5'-triphosphate; D011189:Potassium Chloride; D000255:Adenosine Triphosphate; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases