Regiospecific enzymatic oxygenation of cis‐vaccenic acid during aerobic senescence of the halophilic purple sulfur bacterium Thiohalocapsa halophila

Abstract

A regiospecific oxygenation of the allylic carbon 10 of cis-vaccenic acid has been observed in senescent cells of the halophilic purple sulfur bacterium Thiohalocapsa halophila incubated under aerobic conditions in darkness. The results obtained strongly suggest that these enzymatic processes involve the initial dioxygenase-mediated formation of 1 O-hydroperoxyoctadec-cis-11-enoic acid, which is not accumulated in the cells of T. halophila owing to its high cytotoxic properties. Deuterium labeling and GC-MS analyses enabled us to demonstrate that subsequent enzymatic conversions of this allylic hydroperoxide involved reduction, cleavage, isomerization, and saturation reactions. Some of the specific oxidation products thus formed could constitute potential T. halophila biomarkers.

GC‐MS structural characterization of fatty acids from marine aerobic anoxygenic phototrophic bacteria

“…Determination of cis-and trans-isomers was based on comparison of the retention times with standards. A similar regiospecific oxygenation of the allylic carbon 10 of cis-vaccenic acid has been observed previously in senescent cells of the halophilic purple sulfur bacterium Thiohalocapsa halophila incubated under aerobic conditions in the dark (42). This enzymatic process was attributed to the involvement of a lipoxygenase.…”

“…A similar oxidation process was previously described in the case of the purple sulfur bacterium Thiohalocapsa halophila (42) and attributed to the involvement of a lipoxygenase. This enzymatic attack of cisvaccenic acid seems to be a characteristic of some (aerobic and anaerobic) phototrophic bacteria.…”

“…5, Table 2). The mass spectra of their silylated derivatives were described previously (42). They exhibited a strong fragment ion at m/z 213 corresponding to the cleavage at the carbon-bearing -OSiMe 3 group.…”

“…Lipoxygenases are nonheme iron-containing dioxygenases that catalyze the addition of molecular oxygen to PUFA with a (cis,cis)-1,4-pentadiene system to give an unsaturated FA hydroperoxide (43). Lipoxygenases may also catalyze the oxygenation of monounsaturated FA such as oleic (44)(45)(46)(47), octadec-cis-12-enoic (47), or cis-vaccenic (42) acid. These processes afford mainly hydroxy-, hydroperoxy-, or oxoacids.…”

Regiospecific Enzymatic Oxygenation of cis‐Vaccenic Acid in the Marine Phototrophic Bacterium Erythrobacter sp. strain MG3

“…MG3) we observed an interesting regiospecific enzymatic peroxidation of the allylic carbon 10 of cis-vaccenic acid [8]. A similar phenomenon was reported also in the purple sulfur bacterium Thiohalocapsa halophila incubated under aerobic conditions in the dark [9]. This enzymatic attack of cisvaccenic acid, which seems to be a characteristic of some (aerobic and anaerobic) phototrophic bacteria, was attributed to the involvement of a dioxygenase.…”