Regio- and stereoselective oxygenations by adult human liver flavin-containing monooxygenase 3. Comparison with forms 1 and 2.
The cDNA for the adult human liver flavin-containing monooxygenase (form 3) (FMO3) was cloned, sequenced, and expressed in Escherichia coli. The cDNA-expressed FMO3 was used to investigate the regio- and stereoselective N- and S-oxygenation of a number of tertiary amines and sulfides, respectively. For comparison, the N- and S-oxygenation of the same chemicals and drugs were examined with adult human liver microsomes from a normal healthy female donor and FMO1 from pig liver and FMO2 from rabbit lung. Both cDNA-expressed FMO3 and adult human liver microsomes N-oxygenated trifluoperazine or 10-(N,N-dimethylaminoalkyl)-phenothiazines with similar substrate specificities. The substrate specificity for FMO3 differed, however, from that of pig liver FMO1. Nucleophilic sulfur-containing compounds [i.e., thiobenzamide, (4-bromophenyl)-1,3-oxathiolane, and 2-methyl-1,3-benzodithiole] were efficiently S-oxygenated by cDNA-expressed FMO3 and adult human liver microsomes. Stereoselective S-oxygenation of (+)- and (-)-(4-bromophenyl)-1,3-oxathiolane and 2-methyl-1,3-benzodithiole was therefore investigated. In general, the stereoselectivity observed for S-oxygenation in the presence of FMO3 was similar to that observed in the presence of adult human liver microsomes. In most cases examined, however, the stereoselectivity for S-oxygenation was quite distinct from that observed for pig liver FMO1. We conclude that FMO3 is the major form of FMO active in adult human liver. Because the stereoselectivity for X-oxygenation and the substrate specificity for tertiary amine N-oxygenation by cDNA-expressed FMO3 are distinct from those of pig liver FMO1, we conclude that the binding channel for each isoform is quite different.(ABSTRACT TRUNCATED AT 250 WORDS)
Lomri
N
N
Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco 94143-0446.
Yang
Z
Z
Cashman
J R
JR
D000328:Adult; D000818:Animals; D018076:DNA, Complementary / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D005260:Female; D015870:Gene Expression; D006801:Humans; D008099:Liver / Q000201:enzymology*; D008862:Microsomes, Liver / Q000201:enzymology; D010105:Oxygenases / Q000737:chemistry*; D011817:Rabbits; D013237:Stereoisomerism; D013379:Substrate Specificity; D013552:Swine
D018076:DNA, Complementary; D010105:Oxygenases; C020066:dimethylaniline monooxygenase (N-oxide forming)