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  • Localization of Cys-344 on the (Ca(2+)-Mg(2+)-ATPase of sarcoplasmic reticulum using resonance energy transfer.

Localization of Cys-344 on the (Ca(2+)-Mg(2+)-ATPase of sarcoplasmic reticulum using resonance energy transfer.

Biochimica et biophysica acta (1993-04-08)
A M Mata, H I Stefanova, M G Gore, Y M Khan, J M East, A G Lee
ABSTRACT

4-Bromomethyl-6,7-dimethoxy-coumarin labels the (Ca(2+)-Mg(2+)-ATPase of skeletal muscle sarcoplasmic reticulum at Cys-344. Resonance energy transfer has been used to measure the distance between this site and Lys-515 labelled with fluorescein isothiocyanate as about 37 A. The height of Cys-344 above the phospholipid/water interface has been measured by resonance energy transfer for the ATPase reconstituted into bilayers containing fluorescein-labelled phosphatidylethanolamine; the height was found to be about 45 A. None of these distances was found to alter on changing pH, or on addition of Mg2+, Ca2+ or vanadate. Quenching of the fluorescence of the coumarin-labelled ATPase with KI suggested that the fluorophore is not fully exposed on the ATPase.