Journal of Lipid Research, Vol. 9, 492-500, July 1968
Copyright © 1968 by Lipid Research, Inc.

Relation of lipid structure of sarcotubular vesicles to Ca⁺⁺ transport activity

B. P. Yu , F. D. Demartinis , and E. J. Masoro

Department of Physiology and Biophysics, Woman's Medical College of Pennsylvania, Philadelphia, Pennsylvania 19129

The role of lipids of the sarcotubular membranes in their Ca⁺⁺ uptake and Mg-ATPase activities was investigated. Treatment of the membranes with phospholipase C inhibits both processes. Treatment with phospholipase A and phospholipase D, which results in massive hydrolysis of the sarcotubular phospholipids, does not inhibit either the Ca⁺⁺ uptake or the Mg-ATPase activities, nor does treatment with the polyene antibiotics affect these processes. Essential fatty acid deficiency alters sarcotubular membrane lipids; they contain much less stearic, linoleic, and arachidonic acids and much more oleic and eicosatrienoic acids than normally, but do not lose the ability to actively sequester Ca⁺⁺. It is concluded that neither nonpolar lipids nor the nonpolar regions of polar lipids are involved in Ca⁺⁺ sequestering and Mg-ATPase activities of the sarcotubular membranes.

Of the polar components, the phosphoryl moiety of the phospholipids is required for both activities. However, the phosphoryl group appears to be required for the maintenance of the membranous structure necessary for Ca⁺⁺ sequestration rather than serving specifically in the active transport process. That treatment with phospholipase D, which results in the conversion of much of the sarcotubular phospholipid from a dipolar to an anionic structure, does not affect Ca⁺⁺ uptake activity is a most remarkable finding.

Supplementary key words sarcotubular membranes • active Ca⁺⁺ transport • Mg-ATPase • phospholipase C • phospholipase A • phospholipase D • polyene antibiotics • essential fatty acid deficiency • phospholipids • cholesterol • electron micrographs

Submitted on January 8, 1968
Accepted on March 7, 1968

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