Acid and base hydrolysis of lipid A from Enterobacter agglomerans as monitored by electrospray ionization mass spectrometry: pertinence to detoxification mechanisms.
Lipopolysaccharides (LPS), which are endotoxins found in the cell wall of Gram-negative bacteria, are common components of organic dusts that cause or contribute to symptoms associated with organic dust diseases. The lipid A subgroup within LPS is believed to be responsible for the toxicity. Acid and base treatments, which can be effective detoxification methods, were performed on lipid A from Enterobacter agglomerans (EA), a bacterium commonly found in field cotton. Negative-ion electrospray ionization mass spectrometry was employed to characterize the post-treatment structural changes to lipid A. Acid treatment (1% acetic acid, 100 degrees C) hydrolyzed the ester side-chains of lipid A. It was found that the ester-linked palmitoyl group was the most labile to acid hydrolysis. Hydrolysis of the palmitoyl moiety conformed to pseudo-first-order chemical reaction kinetics with a rate constant for decomposition of heptacyl-lipid A from Enterobacter agglomerans of approximately 3.3 x 10(-3) min-1. An order of lability of lipid A acyl side-chains to acid hydrolysis was also deduced: R4' (palmitoyl) > R1' (myristoyl or hydroxymyristoyl) > R3 (hydroxymyristoyl at position 3) > R1 (oxymyristoyl group at position 3') > R2' (lauroyl). Base treatment (0.05 M NaOH in 95% EtOH, 65 degrees C) was shown to be more effective at cleaving ester-linked side-chains. In addition, mass spectral evidence suggests that opening of the pyranose rings of the disaccharide backbone of lipid A and/or removal of the phosphoryl groups may be occurring during base treatment. This study sheds light on mechanistic aspects of treatment procedures leading to the detoxification of endotoxins.
Wang
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Department of Chemistry, University of New Orlcans, Lakefront, Louisiana 70148, USA.
Cole
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D000143:Acids; D000468:Alkalies; D002236:Carbohydrate Conformation; D002240:Carbohydrate Sequence; D004731:Endotoxins / Q000737:chemistry* / Q000633:toxicity; D004754:Enterobacter / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D007700:Kinetics; D008050:Lipid A / Q000737:chemistry* / Q000633:toxicity; D013058:Mass Spectrometry / Q000379:methods*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009227:Myristic Acids; D010168:Palmitates
D000143:Acids; D000468:Alkalies; D004731:Endotoxins; D008050:Lipid A; D009227:Myristic Acids; D010168:Palmitates