Biosynthesis of Trimethylammonium Compounds in Aquatic Animals: IV. Precursors of Trimethylamine Oxide and Betaine in Marine Teleosts

Abstract

An in-vivo study was made of potential precursors of trimethylamine oxide (TMAO) in marine teleosts (lemonsole, Parophyrs vetulus, and starry flounder, Platichthys stellatus). C14-labelled compounds were adminstered intraperitoneally and the incorporation of tracer into TMAO, isolated from the whole body, was determined. Trimethylamine (TMA)-C14 was a much better precursor than the other other compounds tested. A limited labelling of TMAO was observed after administration of [gamma] -butyrobetaine-methyl-C14, betaine-methyl-C14 and methionine-methylamine-C14, carnitine-methyl-C14, glycine-2-C14, sodium formate-C14, sodium acetate-1-C14, sodium acetate-2-C and NaHCO3-C . The conversion of choline-methyl-C14 to TMAO was higher after intraperitoneal than after intramuscular injection and only trace amounts of radioactivity were found after intravenous injection. The results provide support for formation of TMAO in fish by oxidation of TMA but they give no clear indication for metabolic pathways leading to this oxidative step. Betaine was isolated from fish after admin-istration of choline-methyl-C14, methionine-methyl-C14 and glycine-2-C . Evidence of extensive conversion of choline to betaine was obtained. Betaine also was labelled after administration of methionine-methyl-C14, but only a limited degree of labelling was observed after administration of glyclne-2-C14. The results indicate that betaine is formed by oxidation of choline in fish. A modification of the Dragen-dorff reagent for use as a spray for detecting trimethylammonium compounds on paper chromatograms is described.