Fig. 1.

Known pathways for the formation of trimethylamine (TMA) from dietary choline and carnitine. The key enzymes responsible for TMA production indicated in the figure are: CntAB, carnitine monooxygenase [17] which is analogous to YeaW; CutCD, choline-TMA lyase [10] and GrdH, glycine betaine reductase [20]. Choline to glycine betaine is mediated by the Bet pathway [48], a pathway from carnitine to glycine betaine has been proposed, but has yet to be elucidated [49], [50]. Additionally shown in dark grey the TorA, trimethylamine N-oxide reductase [21] and TMAO formation pathway FMO, flavin-containing monooxygenase are critical to TMA cycling, but are not the focus of this review [51], [52].