The Structure of an Ornithine-containing Lipid from Thiobacillus thiooxidans

Abstract

Abstract The structure of an ornithine-containing lipid from Thiobacillus thiooxidans has been elucidated. Methanolysis of the lipid released methyl cis-11,12-methylene-2-hydroxy-octadecanoate. Acid hydrolysis of the residue yielded ornithine and a mixture of fatty acids, the major components of which were 3-hydroxyhexadecanoic and 2-hexadecenoic acids. Identification of the 3-hydroxy fatty acid was based on the thin layer chromatographic mobilities of the acid, its methyl ester, the methyl ether, and acetate derivatives of its methyl ester, on the equivalent chain lengths of the derivatives of the acid and the acid obtained by oxidation of the natural acid with permanganate, and on mass spectral studies. Similar techniques were used for the identification of 2-hexadecenoic acid. The minor fatty acids and the 2-hexadecenoic acid were found to be degradation products of the 3-hydroxy acid. A 1:1:1 molar ratio was determined for the three lipid components, ornithine, cis-11,12-methylene-2-hydroxyoctadecanoic acid, and 3-hydroxyhexadecanoic acid. Evidence for an ester linkage between the carboxyl group of the 2-hydroxy fatty acid and the hydroxyl group of the 3-hydroxy acid was obtained by infrared spectra, degradation of 14C-labeled lipid, and reactions of the lipid with NaOCH3 and NH2OH. The 3-hydroxyhexadecanoic acid was determined to be attached to the α-amino group of ornithine through an amide bond. This conclusion was supported by the conditions necessary to achieve hydrolysis, infrared spectra, end group analysis with dansyl chloride, and nonaqueous titrations. Data obtained in this investigation indicated that the δ-amino group and the carboxyl group of ornithine were free and that the extracted lipid existed as a zwitterion. Elemental analysis and unit weight determinations were consistent with the proposed structure.