Cytochrome P450 monooxygenase; part of the gene cluster that mediates the biosynthesis of fumosorinone, a 2-pyridone alkaloid that acts as an inhibitor of protein tyrosine phosphatase 1B which is implicated asa negative regulator of insulin receptor signaling and a potential drug target for the treatment of type II diabetes and other associated metabolic syndromes (PubMed:25857260). The polyketide-amino acid backbone of fumosorinone is first assembled by the PKS-NRPS hybrid fumoS (PubMed:25857260). The PKS modules condense one acetyl-CoA starter unit with 7 malonyl-CoA units, programmed C-methylations occurring after the first 3 and the sixth extensions, and cycles of full reduction occurring after the first 2 extensions (Probable). Because fumoS lacks a designated enoyl reductase (ER) domain, the required activity is provided the enoyl reductase fumoC (Probable). Upon formation of the polyketide backbone on the thiotemplate, the polyketide is transferred to the NRPS module and linked to tyrosine to produce the acyltetramic acid intermediate called prefumosorinone A (Probable). The cytochrome P450 monooxygenase fumoA then probably catalyzes an unprecedented oxidative ring expansion of prefumosorinone A to form prefumosorinone B which contains the 2-pyridone core of fumosorinone (Probable). The cytochrome P450 monooxygenase fumoB might hydroxylate the nitrogen of prefumosorinone B, but not the acyltetramic acid prefumosorinone A, to form fumosorinone (Probable). Secondary metabolite biosynthesis. Belongs to the cytochrome P450 family.