LIPID EXTRACTS FROM MEMBRANES OF ACHOLEPLASMA-LAIDLAWII A GROWN WITH DIFFERENT FATTY-ACIDS HAVE A NEARLY CONSTANT SPONTANEOUS CURVATURE

X-ray diffraction methods were used to explore the variation in the sp ontaneous curvature of lipid extracts from Acholeplasma laidlawii stra in A-EF22 grown with different mixtures of palmitic acid and oleic aci d. It was shown that the cells respond to the different growing condit ions by altering the polar head group compositions in order to keep th e phase transition between lamellar and nonlamellar structures within a narrow temperature range. This has been interpreted to mean that the membrane lipids are adjusted toward an optimal packing (Lindblom et a l. (1986) Biochemistry 25, 7502). Here it is shown that for these extr acts, the membrane curvature is kept within a narrow range (58-73 Angs trom), compared to the range in curvatures exhibited by pure lipids ex tracts from the membrane (17-123 Angstrom). These observations support the hypothesis (Gruner (1989) J. Phys. Chem. 93, 7562) that the spont aneous curvature is a functionally important membrane parameter which is regulated by the organism and is likely to be one of the constraint s controlling the lipid composition of the bilayer.