Direct fluorescence measurements of Mg2+ binding to sarcoplasmic reticulum ATPase.
In the absence of calcium, interaction of magnesium with SR-ATPase induced a blue shift in intrinsic fluorescence emission. This Mg2+-induced fluorescence change was pH-dependent and an apparent Mg dissociation constant of 5 mM was found at pH 7. Equilibrium studies showed that magnesium competes for the high affinity Ca2+ binding sites and stopped flow measurements of the transient kinetics indicated a multistep interaction between magnesium and the calcium pump. These results suggest that magnesium drives the sarcoplasmic reticulum atpase toward an E.Mg species which might be a dead-end complex.
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D011485:Protein Binding; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013050:Spectrometry, Fluorescence
D000251:Adenosine Triphosphatases; D008274:Magnesium; D002118:Calcium