title: Effect of compound 48/80 and ruthenium red on the Ca2+-ATPase of sarcoplasmic reticulum.
abstract: The effects of the condensation product of N-methyl-p-methoxyphenethylamine with formaldehyde (compound 48/80) and ruthenium red on the partial reactions of the catalytic cycle of the sarcoplasmic reticulum Ca2+-ATPase of skeletal muscle were studied. The ATPase activity and both Ca2+ and Sr2+ uptake were inhibited by compound 48/80 when oxalate was used as a precipitating agent. The degree of inhibition decreased when oxalate was replaced by orthophosphate as the precipitating anion. Both the fast Ca2+ efflux and the synthesis of ATP observed during reversal of the Ca2+ pump were inhibited by compound 48/80. Inhibition of the reversal of the Ca2+ pump was caused by a competition between compound 48/80 and orthophosphate for the phosphorylation site of the enzyme. The fast Ca2+ release promoted by arsenate was impaired by compound 48/80. Ruthenium red competes with Ca2+ for the high affinity binding site of the Ca2+-ATPase, but did not interfere with the binding of Ca2+ to the low affinity binding site of the enzyme. In presence of Ca2+ concentrations higher than 5 microM, ruthenium red in concentrations up to 200 microM had no effect on both ATPase activity and Ca2+ uptake. However, the fast Ca2+ efflux promoted by arsenate and the fast Ca2+ efflux coupled with the synthesis of ATP observed during the reversal of the Ca2+ pump were inhibited by ruthenium red, half-maximal inhibition being attained in presence of 10-20 microM ruthenium red. In contrast to the effect of compound 48/80, ruthenium red did not inhibit the phosphorylation of the enzyme by orthophosphate. The ATP in equilibrium with Pi exchange catalyzed by the Ca2+-ATPase in the absence of transmembrane Ca2+ gradient was also inhibited by ruthenium red.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D007700:Kinetics; D009132:Muscles / Q000201:enzymology; D010710:Phosphates / Q000378:metabolism; D010766:Phosphorylation; D011817:Rabbits; D012428:Ruthenium / Q000494:pharmacology*; D012430:Ruthenium Red / Q000494:pharmacology*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013324:Strontium / Q000378:metabolism; D003189:p-Methoxy-N-methylphenethylamine / Q000494:pharmacology*
chemical_list: D010710:Phosphates; D012430:Ruthenium Red; D003189:p-Methoxy-N-methylphenethylamine; D012428:Ruthenium; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D002118:Calcium; D013324:Strontium