title: Demonstration of the simultaneous activation of Ca2+-independent and Ca2+-dependent ATPases from rat skeletal muscle microsomes.
abstract: The activation of the Ca2+-independent (basal) ATPase from rat skeletal muscle microsomes is demonstrated in the presence of enough Ca2+ to provide the simultaneous activation of the (Ca2+ + Mg2+)-ATPase. It was achieved taking advantage of the delayed inorganic phosphate (Pi) release due to the formation of a phosphoenzyme complex during the Ca2+-dependent enzymatic cycle, which is evidenced in fast experiments. The microsomes were immobilized on a filter and perfused at constant flow with an incubation medium which was briefly interrupted with a pulse of appropriate reactants to activate the ATPases, at 2 degrees C. Successive samples were collected after passing through the filter, at approx. 0.1 s intervals. The Pi effluent profile coincides with the pattern of the pulse when it activates only the Ca2+-independent ATPase, it appears delayed when the pulse activates only extra Pi production by the (Ca2+ + Mg2+)-ATPase, and it includes a rapid and a delayed component when both Ca2+-independent and Ca2+-dependent ATPases are activated simultaneously by the pulse.
authors.affiliation: Cátedra de Biofísica, Facultad de Odontología, Universidad de Buenos Aires, Argentina.
authors.forename: C A
authors.initials: CA
authors.lastname: Obejero Paz
authors.forename: D A
authors.initials: DA
authors.lastname: González
authors.forename: G L
authors.initials: GL
authors.lastname: Alonso
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D008861:Microsomes / Q000201:enzymology; D009132:Muscles / Q000201:enzymology*; D010710:Phosphates / Q000378:metabolism; D051381:Rats
chemical_list: D010710:Phosphates; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D002118:Calcium