LIPID STRUCTURE AND CA2+-ATPASE FUNCTION

Effects of lipid structure on the function of the Ca2+-ATPase of skele tal muscle of sarcoplasmic reticulum are reviewed. Binding of phosphol ipids to the ATPase shows little specificity. Phosphatidylcholines wit h short (C14) or long (C24) fatty acyl chains have marked effects on t he activity of the ATPase, including a change in the stoichiometry of Ca binding. Low ATPase activity in gel phase lipid follows from low ra te of phosphorylation. Phosphatidylinositol 4-phosphate increases ATPa se activity by increasing the rate of dephosphorylation of the phospho rylated ATPase. Stimulation is not seen with other anionic phospholipi ds; phosphatidic acid decreases ATPase activity in a Mg2+-dependent ma nner.