Effect of pH on the activity of the Ca2+ + Mg2(+)-activated ATPase of sarcoplasmic reticulum.
A kinetic model for the Ca2(+) + Mg2(+)-activated ATPase of sarcoplasmic reticulum was presented in a previous paper [Stefanova, Napier, East & Lee (1987) Biochem. J. 245, 723-730]. Here, that model is modified to account for the pH-dependence of ATPase activity and for the effects of Mg2+ on activity at high pH. It is shown that effects of Mg2+ on measurements of ATPase activity as a function of ATP concentration at pH 8.0 and pH 8.5 are consistent with binding of Mg2+ to the Ca2(+)-binding sites on the phosphorylated ATPase, such binding inhibiting dephosphorylation of the ATPase. It is also shown that slow dissociation of Ca2+ from the phosphorylated ATPase is consistent with the previously published model.
Michelangeli
F
F
Department of Biochemistry, University of Southampton, U.K.
Colyer
J
J
East
J M
JM
Lee
A G
AG
D000818:Animals; D001665:Binding Sites; D017301:Ca(2+) Mg(2+)-ATPase / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D005260:Female; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008433:Mathematics; D008962:Models, Theoretical; D009132:Muscles / Q000201:enzymology; D010766:Phosphorylation; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
D017301:Ca(2+) Mg(2+)-ATPase; D000252:Calcium-Transporting ATPases; D008274:Magnesium; D002118:Calcium