LOCALIZATION OF THE HINGE REGION OF THE CA2-ATPASE OF SARCOPLASMIC-RETICULUM USING RESONANCE ENERGY-TRANSFER()

The Ca2+-ATPase of skeletal muscle sarcoplasmic reticulum can be label led at Cys-670 and Cys-674 with 5-[[2-[(iodoacetyl) amino]ethyl]amino] napthalene-1-sulphonic acid (IAEDANS). Resonance energy transfer has b een used to measure the distance between Cys-670/Cys-674 and Glu-439 l abelled with 5-(bromomethyl)fluorescein as 40 Angstrom. The height of Cys-670/ Cys-674 above the phospholipid/water interface has been measu red by resonance energy transfer between IAEDANS-labelled ATPase and f luorescein-labelled phosphatidylethanolamine as 54 Angstrom. This loca tes the hinge region of the ATPase close to the mouth of the pore obse rved in the cytoplasmic region of the ATPase in electron micrographs. No significant changes in these distances can be detected by resonance energy transfer on binding Ca2+ or vanadate. The height of the IAEDAN S label above the phospholipid/water interface is the same for bilayer s of dimyristoleoylphosphatidylcholine and dioleoylphosphatidylcholine . Conformation changes on the Ca2+-ATPase appear to be localised to sm all regions of the ATPase.