Photochemical oxidation and autoxidation of chlorophyll phytyl side chain in senescent phytoplanktonic cells: potential sources of several acyclic isoprenoid compounds in the marine environment.

Visible light-induced degradation of the chlorophyll phytyl side chain was studied in senescent cells of two phytoplanktonic strains (Skeletonema costatum and Thalassiosira weissflogii). Particular attention was paid to the induction of autoxidation processes on the phytyl chain and its photoproducts by photochemically produced hydroperoxides. The combination of photochemical oxidation and autoxidation reactions resulted in the production of several acyclic isoprenoid compounds that have been unambiguously identified by comparison of their retention times and mass spectra with those of appropriate standards.

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

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.