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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: (i) dimerization of the anthracene‐labelled lipids in the membrane by irradiation of the intact cells at 360 nm; (ii) extraction of the lipids and thin‐layer chromatography in the first dimension to separate the various lipid dimers from the monomers; (iii) partial dedimerization of the lipid dimers by illumination of the chromatogram at around 250–280 nm; (iv) 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.

1,2-Didodecanoyl-sn-glycero-3-phosphoryl-1'-(3'-O-L-alanyl)-sn-glycerol (Ala-PG) has been synthesized. Its ionic properties have been studied at the air-water interface through film compressions and surface potential measurements as a function of subphase pH and ionic content (NaCl, Na2MoO4, CaCl2). The existence of the polar head in a loop conformation allowing for interactions between phosphate and amino groups is suggested. Ionic properties of Ala-PG clearly depended on subphase ionic strength but no specific interactions between either cations or anions in the subphase and phosphate or amino groups in the film could be detected. Results are interpreted in terms of ion-pair interactions at the interface between these two groups and anions and cations from the subphase. Occurrence of charge separation between these two groups, induced by increasing subphase ionic strength, is postulated. Since the molecular packing appeared independent of the subphase ionic content over a large domain of pH (3–8) and surface pressure (π> 5 dyne/cm) and since the lipid can be considered as zwitterionic or slightly positive below pH 5–6, it is suggested that in the parent bacteria, grown under acidic conditions, Ala-PG could play a role in maintaining the membrane intergrity and in preventing the passive diffusion of protons.