Heterogeneity of phospholipid composition in the bacterial membrane.

Heterogeneity in the distribution or binding of the membrane phospholipids was demonstrated in the membrane fragments released from Haemophilus parainfluenzae by treatment with ethylenediaminetetraacetic acid (EDTA)-tris(hydroxymethyl)-aminomethane (Tris). The membrane fragments released early in the EDTA-Tris treatment contained two- to fivefold higher proportions of cardiolipin and phosphatidylglycerol and less phosphatidylethanolamine as well as phospholipids with threefold lower specific activity of the phospholipid phosphate after a short pulse of (32)P than were found in the residue. Heterogeneity was best demonstrated with shorter EDTA-Tris treatments and shorter periods of growth with (32)P. EDTA-Tris treatment appeared to progressively strip phospholipids from the cells that were synthesized at progressively later times.