title: Effect of phospholipid substitution on the mobility of spin labels bound to the ATPase of sarcoplasmic reticulum.
abstract: The mobility of spin labels covalently bound to the Ca2+-transport ATPase (ATP phosphohydrolase [EC 3.y.1.3]) was studied by electron spin-resonance spectroscopy in purified ATPase and reconstituted vesicles. The purified ATPase of sarcoplasmic reticulum of rabbit skeletal muscle was covalently labeled with maleimide spin-labels of different chain length and the phospholipids were exchanged for dipalmitoylphosphatidylcholine. The spectrum of the short-chain maleimide spin-label, bound to purified ATPase indicates reduced mobility after substitution of endogenous phospholipids with dipalmitoylphosphatidylcholine. With the long-chain maleimide derivative no difference was detected in the spectra, measured at 20-35 degrees C temperature before and after substitution with dipalmitoylphosphatidylcholine. Below 10 degrees C temperature the substitution with dipalmitoylphosphatidylcholine decreased the mobility of the prove, indicating that the microviscosity of environment in the vicinity of nitroxide groups was influenced by changes in the fatty acid composition. With both short and long chain spin-labels bound to purified ATPase adn sarcoplasmic reticulum vesicles the amplitude of weakly immobilized component sharply decreased in media containing 20-50% glycerol. Therefore, the mobility of covalently bound nitroxide group in short or long chain maleimide derivatives is also sensitive to the viscosity of the water phase.
mesh_terms: D000818:Animals; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D007700:Kinetics; D009132:Muscles / Q000201:enzymology; D011663:Pulmonary Surfactants / Q000494:pharmacology*; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013113:Spin Labels; D013696:Temperature
chemical_list: D011663:Pulmonary Surfactants; D013113:Spin Labels; D000252:Calcium-Transporting ATPases