THE FLAVIN-CONTAINING MONOOXYGENASES IN RAT-LIVER - EVIDENCE FOR THE EXPRESSION OF A 2ND FORM DIFFERENT FROM FMO1

A second form of rat liver FMO, FMO-A, was separated and purified by c hromatography on Blue Sepharose Fast flow 6. This FMO-A is different f rom FMO1 by antigenic properties (anti-FMO-A did not cross-react with FMO1, and reciprocally) and by catalytic properties (the K-m,for trime thylamine was 3.8 mu M and 141.4 mu M for FMO-A and FMO1, respectively ; the K-m for imipramine was 536 mu M and 17.4 mu M for FMO-A and FMO1 , respectively). Furthermore, N-terminal amino sequencing revealed dif ferences in the primary structure of these two FMOs although they both contained the highly conserved FAD-binding domain (Gly-X-Gly-X-X-Gly) . (C) 1995 Academic Press, Inc.