endoplasmic reticulum membrane,
endoplasmic reticulum lumen
Trimethylamine (TMA) is present in the diet (in fish) but primarily formed in vivo from the breakdown of choline. It is N-oxidised by FMO3 in the liver, the major isoform active towards TMA. Defects in FMO3 can cause trimethylaminuria (TMAU; MIM:602079, fish-odour syndrome), a human genetic disorder characterised by an impaired ability to convert the malodourous TMA to its odourless N-oxide (Treacy et al. 1998). Mutations that cause TMAU include M66I, P153L, R492W, N61S and E32K (Zhang et al. 2003, Yeung et al. 2007).