TETRAOLEOYLPYROPHOSPHATIDIC ACID - A 4 ACYL-CHAIN LIPID WHICH FORMS AHEXAGONAL-II PHASE WITH HIGH CURVATURE

Tetraoleoylpyrophosphatidic acid (bis phosphatidic acid), when hydrate d in aqueous buffer, was shown to form an inverted hexagonal phase usi ng P-31 NMR. Low-angle x-ray diffraction provided verification of the formation of this phase in dilute aqueous buffer and in 2 M NaCl and p ermitted comparison of the tube diameter with that of cardiolipin in 2 M NaCl. By using the water cylinder diameters for tetraoleoylpyrophos phatidic acid, bovine cardiolipin, chloroplast monogalactosyldiglyceri de, and dioleoyl phosphatidylethanolamine as a means of estimating the spontaneous curvatures, tetraoleoylpyrophosphatidic acid was shown to exhibit the greatest curvature of any of the above lipids, equaled on ly by the calcium salt of cardiolipin. Inverted micelles of hydrated t etraoleoylpyrophosphatidic acid and of cardiolipin in tetradecane were approximately the diameter of the inverted hexagonal tubes. A rationa le is given for the differences.