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Fatty Acid Composition and Oxylipin Enzymatic Production in the Tropical Coenocytic Marine Chlorophyte Acetabularia crenulata

  • Author(s): Santiago-Vázquez, Lory Z.
  • et al.
Abstract

Acetabularia crenulata was utilized as a model to study in vitro and in vivo enzymatic oxylipin production.

The fatty acid composition of A. crenulata was analyzed. Cell free extracts were derivatized by two methylation procedures, saponification and diazomethane, to compare how the two influenced fatty acid composition. Qualitatively, no significant differences were observed. The major fatty acids observed in both preparations were palmitic, palmitoleic, oleic, linoleic, linolenic and octadecatetraenoic acid. No major differences were observed in fatty acid composition of cell free extracts of alga grown in the lab and of alga collected in the wild. The fatty acid composition of chloroplasts showed the biggest difference in composition when compared to other preparations, excluding palmitoleic and octadecatetraenoic acid from the major fatty acids. The amount of C16:3 was very low in chloroplast preparations, therefore it was hypothesized that chloroplasts of A. crenulata followed the "eukaryotic" for MGDG synthesis.

In general, the fatty acid composition is similar to that of other marine Chlorophytes.

Cell free extracts and live cells incubated with oleic acid were shown to produce the LOX metabolites 13-HODE, 13-HOTrE and 8-HETE. 13-HODE was found to be an endogenous metabolite. The same preparations incubated with arachidonic acid synthesized 5-, 8-, 11-, 12-, and 15-HETE. In addition, cell free extracts incubated with arachidonic acid also synthesized 13-HODE and 15- HEPE. The data shows enzymatic activity of different LOX isoenzymes, with a preference for w-6 oxidation.

In vitro HETE production over time displayed classic enzyme kinetics. In vivo HETE production in the dark and in the light demonstrated that some oxylipins are preferentially synthesized inside the chloroplasts while others are preferentially synthesized outside. The possible production of an LT-type molecule outside the chloroplast was proposed. A role of hydroxy fatty acids in growth was not observed.

In conclusion, LOX-mediated in vitro and in vivo oxylipin production was demonstrated in A. crenulata and a possible role of these metabolites in the physiological processes of the organism was suggested.

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