Human flavin-containing monooxygenase 1 and its long-sought hydroperoxyflavin intermediate

Abstract

Out of the five isoforms of human flavin-containing monooxygenase (hFMO), FMO1 and FMO3 are the most relevant to Phase I drug metabolism. They are involved in the oxygenation of xenobiotics including drugs and pesticides using NADPH and FAD as cofactors. Majority of the characterization of these enzymes has involved hFMO3, where intermediates of its catalytic cycle have been described. On the other hand, research efforts have so far failed in capturing the same key intermediate that is responsible for the monooxygenation activity of hFMO1. In this work we demonstrate spectrophotometrically the formation of a highly stable C4ahydroperoxyflavin intermediate of hFMO1 upon reduction by NADPH and in the presence of O2. The measured half-life of this flavin intermediate revealed it to be stable and not fully reoxidized even after 30 minutes at 15 °C in the absence of substrate, the highest stability ever observed for a human FMO. In addition, the uncoupling reactions of hFMO1 show that this enzyme is <1% uncoupled in the presence of substrate, forming small amounts of H2O2 with no observable superoxide as confirmed by EPR spin trapping experiments. This behaviour is different from hFMO3, that is shown to form both H2O2 and superoxide anion radical as a result of ~50% uncoupling. These data are consistent with the higher stability of the hFMO1 intermediate in comparison to hFMO3. Taken together, these data demonstrate the different behaviours of these two closely related enzymes with consequences for drug metabolism as well as possible toxicity due to reactive oxygen species.

Metabolomics Assessment of Volume Overload-Induced Heart Failure and Oxidative Stress in the Kidney

“…Though the liver is the primary site of endogenous taurine synthesis, smaller amounts are also produced in peripheral organs, including the kidneys [45]. In addition to obtaining taurine from the diet, most taurine can also be synthesized from hypotaurine by flavin-containing monooxygenase (FMO1) in the livers of mice [46]. However, this synthesis does not occur in the livers of adult humans.…”

Exploring the role of flavin-dependent monooxygenases in the biosynthesis of aromatic compounds

“…Groups G and H are also single-component with the ability to reduce the flavin cofactor by oxidating substrates [26,27]. The catalytic mechanism of FDM has been fully reported in detail [28][29][30][31][32]. In brief, the FDM-catalyzed hydroxylation of aromatic compounds can be divided into two parts: the reductive half-reaction for FAD and FMN, and the oxidative half-reaction for substrates [33].…”

Mice, rats, and guinea pigs differ in FMOs expression and tissue concentration of TMAO, a gut bacteria-derived biomarker of cardiovascular and metabolic diseases

“…Extensive research has been conducted to elucidate FMOs biochemical properties, substrate specificities, and functional roles. Among them, FMO5 stands out as it exhibits no activity towards trimethylamine [16][17][18][19][20][21][22][23].…”