Interaction of spin-labelled phosphatidyl choline with Ca-dependent ATPase from sarcoplasmic reticulum

The interaction between 3-acyl-2-(6-doxylpalmitoyl) phosphatidyl choline used as a hydrophobic spin probe and Ca2+-dependent ATPase from sarcoplasmic reticulum membranes of rabbit and carp white skeletal muscles was studied. The spin label incorporation into ATPase preparations was performed at initial steps of ATPase isolation by incubating reticulum membranes with the spin probe in the presence of cholic acid. A comparison of the molecular mobility of the probe incorporated into ATPase preparations and into liposomes formed from ATPase phospholipids demonstrated that the presence of the protein in the membrane produces the same effect on the probe mobility as does the decrease of temperature by 10-15 degrees C. The molecular mobility of the probe in the ATPase preparation is increased during protein thermal denaturation. The breaks on the Arrhenius plots for the probe molecular mobility are revealed at the same temperatures (25 degrees for rabbit reticulum and 16 degrees for carp reticulum) as those for the ATPase activity.