Effect of pH and ionophores on the calcium-pumping ATPase of endoplasmic reticulum microsomes from guinea pig pancreas.
The effects of the proton-ionophore FCCP, the electroneutral calcium-proton ionophore A23187, pH and oxalate on calcium uptake and (Ca-Mg)ATPase activity were assayed in microsomal vesicles prepared from guinea pig pancreas. The results can be summarized as follows: 1) The optimum pH for ATP-dependent calcium uptake was 7, whereas the (Ca-Mg)ATPase activity was maximal at pH 7.5-8; 2) after a time lag of oxalate-insensitivity, oxalate stimulated strongly the ATP-dependent calcium uptake; 3) FCCP uncoupled the process of calcium uptake and ATP hydrolysis; 4) the effects of FCCP on calcium transport and ATPase activity were quite similar to those induced by the calcium ionophore A23187. These results can be explained by the formation of a proton gradient through membrane vesicles during the calcium pumping process.
Galván
A
A
Departamento de Bioquímica, Facultad de Medicina, Universidad de Sevilla, Spain.
Lucas
M
M
D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000201:enzymology; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007476:Ionophores / Q000494:pharmacology*; D008861:Microsomes / Q000201:enzymology; D010070:Oxalates / Q000494:pharmacology; D019815:Oxalic Acid; D010179:Pancreas / Q000201:enzymology*
D007476:Ionophores; D010070:Oxalates; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D000001:Calcimycin; D019815:Oxalic Acid; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium