Differences in enzymatic properties of flavin-containing monooxygenase in brain microsomes of rat, mouse, hamster, guinea pig and rabbit.

To characterize flavin-containing monooxygenase (FMO) in brain microsomes of rat, mouse, hamster, guinea pig and rabbit, profiles of its enzyme activities were investigated by HPLC-fluorometrical assay using benzydamine (BZY) as a substrate. The optimum pH of BZY N-oxidation activity in brain microsomes from rat, mouse, hamster or guinea pig was between 8.5 and 9, though that of the rabbit brain microsomes was near 10.0. The activities were thermally unstable in brain microsomes from all the species examined in the absence of NADPH, but the activity in rabbit brain microsomes was rather thermostable in the presence of NADPH. The activity in rabbit brain microsomes was depressed in the presence of 5 mM n-octylamine. In the presence of MnCl2, the enzyme activity in rabbit brain microsomes was markedly decreased. ZnCl2 markedly decreased the enzyme activities in brain microsomes from rat, mouse and rabbit. It was concluded that BZY N-oxidation activity in brain microsomes from rat, mouse, hamster and guinea pig are similar in enzymatic properties but different from the activity of that of rabbit. These results suggest that common FMO isoform(s) other than FMO4 might exist in the brains of the four rodent species tested.