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The effect of K+ on phosphorylation of the Ca2+-dependent ATPase of the sarcoplasmic reticulum by either Pi or ATP was studied using a millisecond mixing and quenching device. Equilibrium levels of phosphoenzyme formed by Pi were progressively decreased in the presence of increasing K+ concentrations. This effect was more pronounced in empty vesicles than in vesicles previously loaded with calcium. Potassium did not modify the initial rate of enzyme phosphorylation by Pi but increased the rate of phosphoenzyme hydrolysis 4- to 6-fold. Using low ATP concentration (50 micro M), the steady state level of phosphoenzyme was decreased by the addition of K+. This effect disappeared when the ATP concentration was raised to 1 mM.
R M Chaloub, and
L de Meis
June 1979,
Biochimica et biophysica acta,
R M Chaloub, and
L de Meis
March 1983,
The Journal of biological chemistry,
R M Chaloub, and
L de Meis
November 1997,
Annals of the New York Academy of Sciences,
R M Chaloub, and
L de Meis
January 1979,
Biochimica et biophysica acta,
R M Chaloub, and
L de Meis
January 1982,
Annals of the New York Academy of Sciences,
R M Chaloub, and
L de Meis
August 1980,
Archives of biochemistry and biophysics,
R M Chaloub, and
L de Meis
November 2004,
The Journal of biological chemistry,
R M Chaloub, and
L de Meis
January 1988,
Archives of biochemistry and biophysics,
R M Chaloub, and
L de Meis
September 1991,
The Journal of biological chemistry,
R M Chaloub, and
L de Meis
February 2020,
Biochimica et biophysica acta. Biomembranes,
