Monooxygenase that can modify rifampicin, thereby inactivating its antibiotic activity. It constitutes a secondary rifampicin resistance factor. NADPH + O2 + rifamycin SV = H2O + NADP(+) + rifamycin SV para-naphthoquinone carboxamide NADH + O2 + rifamycin SV = H2O + NAD(+) + rifamycin SV para-naphthoquinone carboxamide