Flavin-Containing Monooxygenase FMO

The cellular location (endoplasmic reticulum) reaction stoichiometry is the same, mixed-function oxidation, as for P450, 

FIGURE 2.4 Some uncommon P450 oxidations (Guengerich, 2001). 

Five forms of FMO are found in humans (and several experimental animals). Important physiological substrates have not been established, although some possibilities have been proposed (Ziegler, 1993). An interesting polymorphism involves defects in FMO 3, giving rise to deficient metabolism of trimethylamine and a resulting fish-odor syndrome (Al-Waiz et al., 1987). In contrast to P450, FMOs appear not to be inducible or readily inhibited. 

A practical consideration in working with tissues is that FMOs are not very heat stable, particularly in the absence of pyridine nucleotides (Ziegler and 

Mitchell, 1972), and care should be taken so as not to overlook possible contributions of this enzyme. The C-4a-hydroperoxide is not a strong electrophile, and the range of reaction is limited. In other flavoproteins, this hydroperoxide can produce epoxides or Baeyer-Villiger products (Massey, 2000) but none have been reported for FMOs. FMOs can hydroxylate activated phenyl groups, for example, phenols and anilines (Fig. 2.6) (Frederick et ah, 1982). 

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See also in sourсe #XX -- [ ]

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