CHARACTERIZATION OF FLAVIN-CONTAINING MONOOXYGENASE-5 (FMO5) CLONED FROM HUMAN AND GUINEA-PIG - EVIDENCE THAT THE UNIQUE CATALYTIC PROPERTIES OF FMO5 ARE NOT CONFINED TO THE RABBIT ORTHOLOG

Several full-length clones encoding the human and guinea pig orthologs of flavin-containing monooxygenase 5 (FMO5) have been isolated from l ibraries constructed with hepatic mRNA. The clones were detected by hy bridization with the cDNA encoding FMO5 expressed in rabbit. The human and guinea pig cDNAs encode for proteins of 533 amino acids that cont ain putative pyrophosphate binding domains characteristic of mammalian FMOs. The sequences derived for the human and guinea pig FMO5 protein s are 87% identical and are 85 and 82% identical, respectively, to the sequence of rabbit FMO5. As is the case with other FMOs, FMO5 in huma n and guinea pig is encoded by multiple transcripts. Rabbit FMO5 expre ssed in Escherichia coli was purified and used to elicit antibodies in goat. These antibodies detected FMO5 in samples from livers of adult humans, rabbits, and guinea pigs and fetal livers of humans. The human and guinea pig forms of FMO5 were expressed in E. coli and characteri zed. Neither enzyme effectively catalyzed the metabolism of methimazol e, a general FMO substrate; however, both were active with n-octylamin e. The responses of the human FMO5 and guinea pig FMO5 to detergent, i ons and elevated temperature are all similar to the responses describe d for rabbit FMO5. These results indicate that the unique properties o f FMO5 from rabbit are species-independent and that this form of the f lavin-containing monooxygenase is not readily classified as a drug-met abolizing enzyme. (C) 1995 Academic Press, Inc.