ARRANGEMENT OF PHOSPHATIDYLETHANOLAMINE MOLECULAR-SPECIES IN ESCHERICHIA-COLI MEMBRANES AND RECONSTITUTED LIPIDS AS DETERMINED BY DIMETHYL SUBERIMIDATE CROSS-LINKING OF NEAREST-NEIGHBOR LIPIDS

Dimethylsuberimidate cross-linking has been used to determine the arra ngement of phosphatidylethanolamine (PE) molecular species in Escheric hia coli membranes. No large deviations from random mixing were found in wild-type strain AB1623, either in whole cells or in extracted lipi ds which were reconstituted into multilamellar vesicles. These results suggest, first, that there is little difference in the PE molecular s pecies composition of the three lipid monolayers (the inner and outer monolayers of the inner membrane and the inner monolayer of the outer membrane) which contain significant amounts of PE. Secondly, the resul ts suggest that the molecular species within each monolayer and in the extracted lipids are arranged close to randomly with no tendency for like molecular species to cluster. E. coli strain L8-2, which has a de fect in beta-oxidation and a temperature-sensitive mutation in total f atty acid synthesis, was grown on cis-vaccenate (cis-11,12-octadecenat e) to enrich the cells in divaccenoyl PE. Again, in whole cells or in lipids extracted from whole cells and reconstituted into multilamellar vesicles, the species were close to randomly arranged. However, a con sistent, slight tendency of divaccenoyl species to pair with like spec ies as compared to pairing with the second most common species, vaccen oyl, palmitoleoyl PE, was noted in both extracted lipids and in whole cells.