Nature and Linkages of the Fatty Acids Present in the Lipid‐A Component of Salmonella Lipopolysaccharides

Abstract

Laurie, myristic, palmitic, and 3‐d‐(–)‐myristic acid in a ratio of about 1:1:1:3 are present in the lipid A part of the glycolipid derived from the Re mutant Salmonella minnesota R595. An additional fatty acid, Δ 2‐tetradecenoic acid found in larger amounts after alkaline treatment was recognized as an artifact formed by a β‐elimination reaction from ester‐linked 3‐myristoxy‐myristic acid. Various methods for the stepwise liberation of fatty acids were used to identify their distribution on the backbone of lipid A which consists of β‐1,6‐linked glucosamine disaccharide units substituted at position 3′ with 2‐keto‐3‐eoxyoctonate and at positions 1 and 4′ with phosphate. It was found that the amino groups of the glucosamine residues are substituted by 3‐D‐(–)‐hydroxymyristic acid whose hydroxyl group is free. The three available hydroxyl groups at positions 3, 4, and 6′ of the glucosamine dissaccharide are substituted by equal amounts of lauric, palmitic, and 3‐D‐myristoxymyristic acid and, possibly, by smaller amounts of myristic and unsubstituted 3‐D‐hydroxymyristic acid. A similar structure of lipid A seems to exist in lipopolysaccharides of other Salmonella species.