Chlorobium Aminolipid: a new Membrane Lipid from Green Sulfur Bacteria

Abstract

A preliminary chemical characterization (Olson et al., 1983) of the aminolipid from Chlorobium limicola f. thiosulfatophilum shows that this lipid contains no phosphorus, glycerol, sugar, ornithine or lysine. The lipid has an R_f-value of 0.03 in chloroform-methanol-ammonia (13:5:1 v/v) on silica gel TLC plates. In chloroform-methanol-water (65:25:4) the R_f-value is 0.16. The absorption spectrum indicates bands at 225 and 231 nm, and the fluorescence (maximum emission at 340 nm) shows excitation maxima at 232, 288, and ~325 nm. Acid hydrolysis of the lipid yields fluorescent substances A (ninhydrin positive) and B (negative) in addition to myristic acid (C 14:0). The fluorescence emission and excitation spectra of substance A are very similar to those of the intact lipid. Although these excitation spectra resemble the absorption spectra of 7,8-dihydropterins (bands at ~230, ~280, and 320–330 nm at pH 7), the weight of evidence appears to be against substance A being a pterin. Nevertheless the UV absorption and fluorescence spectra do indicate that the amino moiety (substance A) is an aromatic heterocyclic component.