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Acid and base hydrolysis of lipid A from Enterobacter agglomerans as monitored by electrospray ionization mass spectrometry: Pertinence to detoxification mechanisms
Author(s) -
Wang Yan,
Cole Richard B.
Publication year - 1996
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/(sici)1096-9888(199602)31:2<138::aid-jms263>3.0.co;2-y
Subject(s) - chemistry , hydrolysis , electrospray ionization , lipid a , chromatography , mass spectrometry , organic chemistry , biochemistry , bacteria , biology , genetics
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°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 heptaacyl‐lipid A from Enterobacter agglomerans of ∼3.3 × 10 −3 min −1 . An order of lability of lipid A acyl side‐chains to acid hydrolysis was also deduced: R 4 ′ (palmitoyl) > R 1 ′ (myristoyl or hydroxymyristoyl) > R 3 (hydroxymyristoyl at position 3) > R 1 (oxymyristoyl group at position 3′) > R 2 ′ (lauroyl). Base treatment (0.05 M NaOH in 95% EtOH, 65°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.