Evidence for a homogeneous lateral distribution of lipids in a bacterial membrane

A new photo cross-linking method has been developed for the study of the lateral distribution of lipids in natural membranes, which uses anthracene as a photoactivable group. This method, which rests on the potentiality of anthracene to form covalently bound dimers upon irradiation around 340-380 nm has been applied to the membrane lipids (dimannosyl diacylglycerol, phosphatidylglycerol, phosphatidylinositol) of the bacterium Micrococcus luteus. These glyco- and phospholipids were anthracene labelled by metabolically incorporating the synthetic 9-(2-anthryl)nonanoic acid. The following sequential procedure was used: dimerization of the anthracene-labelled lipids in the membrane by irradiation of the intact cells at 360 nm; extraction of the lipids and thin-layer chromatography in the first dimension to separate the various lipid dimers from the monomers; partial dedimerization of the lipid dimers by illumination of the chromatogram at around 250-280 nm; chromatography in the second dimension to separate the native lipid monomers from the corresponding residual lipid dimers. On account of the occurrence of the 3 hetero dimers phosphatidylglycerol-dimannosyl diacylglycerol, phosphatidylinositol-dimannosyl diacylglycerol and phosphatidylglycerol-phosphatidylinositol after irradiating the cells, it is concluded that in this bacterial membrane, dimannosyl diacylglycerol, phosphatidylglycerol and phosphatidylinositol are homogeneously distributed.