Molecular cloning and characterization of a full-length flavin-dependent monooxygenase from yeast

Eucaryotes contain a class of enzymes called flavin-dependent monooxygenases (FMOs). Unlike mammals, yeast have only a single isoform—yFMO. Deletion mutants suggested that yFMO may play a role in folding proteins which contain disulfide bonds. Recently we detected two nucleotide errors in the GenBank sequences attributed to the yFMO gene. This previously led us to express and characterize a 373-residue catalytically active protein instead of the correct 432-residue enzyme. Here we report the sequencing, expression, and enzyme characterization of the full-length form of yFMO. Comparison of the two forms of yFMO showed similar pH profiles and Km, Kcat, and Vmax values using glutathione as a substrate. These results indicate that the full-length yeast FMO has biochemical and catalytic properties similar to those of the truncated protein. Therefore, it is likely that the hypotheses concerning the enzymeʹs function proposed earlier are still valid.