Cytochrome P450 monooxygenase; part of the gene cluster that mediates the biosynthesis of the isocyanide xanthocillin and its derivatives (PubMed:29844112). The first step of the pathway consists in the conversion of tyrosine into a vinyl-isonitrile intermediate by the isocyanide synthase xanB (PubMed:29844112). Subsequent oxidative dimerization of this intermediate to form xanthocillin may involve the cytochrome P450 monooxygenase xanG, whose expression is coregulated with that of XanB (PubMed:29844112). Xanthocillin can be further modified by the isonitrile hydratase-like protein xanA which introduces N-formyl groups and the methyltransferase xanE which introduces methyl groups, leading to the production of several derivatives including fumiformamide (PubMed:29844112). Finally, fumiformamide can be subject to both oxidative and reductive cyclization to yield melanocins E and F, respectively (PubMed:29844112). Secondary metabolite biosynthesis. Belongs to the cytochrome P450 family.