K+-and Mg2+-dependent hydrolysis of acetyl phosphate catalyzed by the (Ca2+ + Mg2+)-ATPase of sarcoplasmic reticulum

Eduardo N. Chini, Monica Montero-Lomeli, Leopoldo de Meis

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1 Scopus citations


The (Ca2+ + Mg2+-ATPase of sarcoplasmic reticulum catalyzes the hydrolysis of acetyl phosphate in the presence of Mg2+ and EGTA and is stimulated by Ca2+. The Mg2+-dependent hydrolysis of acetyl phosphate measured in the presence of 6 mM acetyl phosphate, 5mM MgCl2, and 2 mM EGTA is increased 2-fold by 20% dimethyl sulfoxide. This activity is further stimulated 1.6-fold by the addition of 30 mM KCl. In this condition addition of Ca2+ causes no further increase in the rate of hydrolysis and Ca2+ uptake is reduced to a low level. In leaky vesicles, hydrolysis continues to be back-inhibited by Ca2+ in the millimolar range. Unlike ATP, acetyl phosphate does not inhibit phosphorylation by Pi unless dimethyl sulfoxide is present. The presence of dimethyl sulfoxide also makes it possible to detect Pi inhibition of the Mg2+-dependent acetyl phosphate hydrolysis. These results suggest that dimethyl sulfoxide stabilizes a Pi-reactive form of the enzyme in a conformation that exhibits comparable affinities for acetyl phosphate and Pi. In this conformation the enzyme is transformed from a Ca2+- and Mg2+-dependent ATPase into a (K+ + Mg2+)-ATPase.

Original languageEnglish (US)
Pages (from-to)152-156
Number of pages5
JournalBBA - Biomembranes
Issue number1
StatePublished - Nov 30 1990


  • (Rabbit)
  • ATPase, (Ca / Mg)-
  • Acetyl phosphate
  • Dimethyl sulfoxide
  • Magnesium ion
  • Potassium ion
  • Sarcoplasmic reticulum

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Cell Biology


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