Cyclopentanone 1,2-monooxygenase (CPMO) from Comamonas (previously Pseudomonas) sp. strain NCIMB 9872 carries out the second step of a degradation pathway that allows the bacterium to use cyclopentanol as a sole carbon source for growth. In the present invention there is reported the localization of the CPMO-encoding gene (cpnB) on a 4.3-kb SphI fragment, the determination of its sequence. The 550-amino acid CPMO polypeptide (Mr, 62,111) encoded by the gene was found to have 36.5% identity with the sequence of cyclohexanone 1,2-monooxygenase (CHMO) of Acinetobacter sp. strain NCIMB 9871. The 62-kDa CPMO was expressed in E. coli as an IPTG-inducible protein.