Chemical properties of thiobarbituric acid-positive substances released from photobacterial lipopolysaccharides during acid hydrolysis

Malondialdehyde and thiobarbituric acid-reactivity as diagnostic indices of lipid peroxidation and peroxidative tissue injury

Increasing appreciation of the causative role of oxidative injury in many disease states places great importance on the reliable assessment of lipid peroxidation. Malondialdehyde (MDA) is one of several low-molecular-weight end products formed via the decomposition of certain primary and secondary lipid peroxidation products. At low pH and elevated temperature, MDA readily participates in nucleophilic addition reaction with 2-thiobarbituric acid (TBA), generating a red, fluorescent 1:2 MDA:TBA adduct. These facts, along with the availability of facile and sensitive methods to quantify MDA (as the free aldehyde or its TBA derivative), have led to the routine use of MDA determination and, particularly, the "TBA test" to detect and quantify lipid peroxidation in a wide array of sample types. However, MDA itself participates in reactions with molecules other than TBA and is a catabolic substrate. Only certain lipid peroxidation products generate MDA (invariably with low yields), and MDA is neither the sole end product of fatty peroxide formation and decomposition nor a substance generated exclusively through lipid peroxidation. Many factors (e.g., stimulus for and conditions of peroxidation) modulate MDA formation from lipid. Additional factors (e.g., TBA-test reagents and constituents) have profound effects on test response to fatty peroxide-derived MDA. The TBA test is intrinsically nonspecific for MDA; nonlipid-related materials as well as fatty peroxide-derived decomposition products other than MDA are TBA positive. These and other considerations from the extensive literature on MDA. TBA reactivity, and oxidative lipid degradation support the conclusion that MDA determination and the TBA test can offer, at best, a narrow and somewhat empirical window on the complex process of lipid peroxidation. The MDA content and/or TBA reactivity of a system provides no information on the precise structures of the "MDA precursor(s)," their molecular origins, or the amount of each formed. Consequently, neither MDA determination nor TBA-test response can generally be regarded as a diagnostic index of the occurrence/extent of lipid peroxidation, fatty hydroperoxide formation, or oxidative injury to tissue lipid without independent chemical evidence of the analyte being measured and its source. In some cases, MDA/TBA reactivity is an indicator of lipid peroxidation; in other situations, no qualitative or quantitative relationship exists among sample MDA content, TBA reactivity, and fatty peroxide tone. Utilization of MDA analysis and/or the TBA test and interpretation of sample MDA content and TBA test response in studies of lipid peroxidation require caution, discretion, and (especially in biological systems) correlative data from other indices of fatty peroxide formation and decomposition.

Characterization ofPseudomonas geomorphus: A novel groundwater bacterium

Strain ABS10, a Gram-negative, pleomorphic bacterium isolated from a pristine aquifer in Ada, Oklahoma, was studied as a candidate for the introduction and expression of plasmid DNA in a native ground water isolate. This organism was originally typed as anArthrobacter sp. due to its morphological phase change and Gram-variable reaction upon Gram staining. The fatty acid methyl ester profile of ABS10 revealed a high similarity withPseudomonas putida. DNA-DNA hybridization showed 81% homology between ABS10 andP. putida. 16S rRNA sequence analysis showed ABS 10 to be a member of the Gamma division of the purple photosynthetic bacteria. The organism has been designatedPseudomonas geomorphus due to its isolation from a subterranean sample and the morphological phase change from rods in young cultures to cocci in older cultures. The broad host range plasmid RP4 was introduced into ABS10 and stably maintained, indicating that RP4 may serve as a vehicle for the introduction of catabolic genes into this organism.

The structure of the heptose-3-deoxy-D-mannooctulosonic-acid region in a mutant form of Aeromonas salmonicida lipopolysaccharide

Lipopolysaccharide was isolated from a phage-selected mutant of a wild strain of Aeromonas salmonicida by the aqueous phenol method. The lipopolysaccharide consisted of the R form, containing per mole, three moles of L-glycero-D-manno-heptopyranose, one mole of 3-deoxy-D-manno-2-octulosonic acid (dOclA) and lipid A. The dOclA was not fully assayable by the thiobarbituric acid methods usually used, but its degradation product was detected, after Smith degradation of the lipopolysaccharide, either as free 3-deoxy-2-heptulosonic acid (after hydrolysis) or substituted by a mannopyranosyl residue derived from heptose. Mass spectrometry indicated that the dOclA existed in the furanose form and was substituted by the heptose trisaccharide through position six. Methylation analysis, chemical degradation, chromium trioxide oxidation and nuclear magnetic resonance spectroscopy were used to identify the structure of the core oligosaccharide as: L alpha DHepp(1----2)L alpha DHepp(1----3)L alpha DHepp(1----6)dOclAf(2----.