Structural and related functional changes in sarcoplasmic reticulum induced by long-chain fatty acids.

The effect of palmitic and oleic acids on Ca2+-ATPase activity in coupled preparations of sarcoplasmic reticulum isolated from rabbit hind leg muscle have been compared with their effects on vesicles uncoupled with Ca2+ ionophore, A23187. Palmitate at 2 microM X mg protein-1 has no significant effect on enzyme activity and does not uncouple catalytic activity from calcium accumulation within the vesicles. Oleic acid at 1 microM X mg protein-1 uncouples the vesicles, whereas 2 microM X mg protein-1 completely inhibits Ca2+-ATPase activity. Fluorescence anisotropy of diphenylhexatriene is not significantly altered by palmitate, but a large transient increase in motion of the probe is observed with addition of oleic acid. The effects of oleic acid on enzyme activity are not mediated via an effect on the bulk properties of the hydrophobic domain of the membrane lipids.