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The substrate is lipid A on the reducing end of the toxic lipopolysaccharide (LPS) of?Salmonella typhimurium?and related organisms. It consists of diglucosamine, ¦Â-D-GlcN-(1¡ú6)-D-GlcN, attached by glycosylation on O-6 of its non-reducing residue, phosphorylated on O-4 of this residue and on O-1 of its potentially reducing residue. Both residues carry 3-(acyloxy)acyl groups on N-2 and O-3. The enzyme from human leucocytes detoxifies the lipid by hydrolysing the secondary acyl groups from O-3 of the 3-hydroxyacyl groups on the disaccharide (LPS). It also possesses a wide range of phospholipase and acyltransferase activities [e.g. EC?3.1.1.4?(phospholipase A2), EC?3.1.1.5?(lysophospholipase), EC?3.1.1.32?(phospholipase A1) and EC?3.1.1.52?(phosphatidylinositol deacylase)], hydrolysing diacylglycerol and phosphatidyl compounds, but not triacylglycerols. It has a preference for saturated C12-C16?acyl groups. |
