Heterogeneity of lipid A.

In a previous study, lipid A from Shigella flexneri was separated into eight distinct fractions by thin-layer chromatography (TLC). In the present investigation, lipid A from different gram-negative bacteria was analyzed by thin-layer chromatography for its heterogeneity and compared with lipid A of S. flexneri. Purified lipid A preparations from six different enterobacterial species were heterogeneous, but based on Rf, comparable bands were found among all preparations. Changing the culture conditions by using two other culture media resulted in very minor changes in the TLC appearance. Different serotypes of Shigella grown under the same conditions also showed very minor differences. Two bands (5 and 8) in each preparation of lipid A comigrated with lysophosphatidylethanolamine and phosphatidylethanolamine, respectively, and both bands were stained with ninhydrin and molybdenum blue. Therefore, phosphatidylethanolamine, and probably lysophosphatidylethanolamine, are common constitutents of unfractioned lipid A preparations, and both phospholipids can occur even in highly purified unfractionated lipid A.