Fig. 1. Diagram showing the possible pathways for trimethylamine (TMA) and trimethylamine oxide (TMAO) production (only abbreviated pathways are drawn). (A) Trimethylalkylammonium compounds (e.g. choline) are degraded to TMA by intestinal microbes (Hebard et al. 1992). (B) Choline is taken up by mitochondria in some animals (Pierce et al., 1997) and converted to glycine betaine via betaine aldehyde. Betaine may subsequently be converted to TMA (Ballantyne, 1997). In both cases (A and B), TMA is oxidized by trimethylamine oxygenase to TMAO.