A cytochrome P450 and an iron-sulfur protein, whose expression was specifically induced during growth of Mycobacterium sp. strain HE5 on morpholine as the sole source of carbon, nitrogen, and energy were purified to apparent homogeneity. Due to the lack of enzymatic activity, carbon monoxide difference spectra and determination of the acid-labile sulfur, respectively, were used to detect the proteins during purification. The cytochrome P450, designated P450(mor), was characterized as a monomer with an apparent molecular mass of 44.7 kDa. The amino acid sequence of an internal peptide comprising 19 amino acids was identical to the sequence derived from a gene encoding a cytochrome P450 from Mycobacterium smegmatis mc(2)155 suggested to be involved in the utilization of piperidine and pyrrolidine. The iron-sulfur protein was characterized as a ferredoxin exhibiting a molecular mass of 6.8 kDa and named Fd(mor). An identity of 48-77% was obtained for the 30 N-terminal amino acids of Fdmor and the corresponding sequences of different 3Fe-4S-ferredoxins known to be involved in P450-dependent reactions. From these data we concluded that growth of Mycobacterium sp. strain HE5 on morpholine led to the expression of a cytochrome P450-dependent monooxygenase system composed of at least two different proteins.