Cytochrome P450 monooxygenase; part of the gene cluster that mediates the biosynthesis of alternapyrone derivatives. Alternapyrone is a decaketide with octa-methylation from methionine on every C2 unit except the third unit. All the domains in the polyketide synthase alt5 are apparently involved in alternapyrone synthesis, that is, the 8 CMeT, 7 KR, 7 DH, and 4 ER reactions in the 9 KS-mediated condensation steps required for alternapyrone synthesis. the alternapyrone produced by alt5 might be intensively modified by cytochrome P450 monooxygenases alt1, alt2 and alt3 and FAD-dependent oxidoreductase alt4 present in the alt gene cluster