Characterization of a New Cyclohexylamine Oxidase From Acinetobacter sp. YT-02

Cyclohexylamine (CHAM) is widely used in various industries, but it is harmful to human beings and the environment. Acinetobacter sp. YT-02 can degrade CHAM via cyclohexanone as an intermediate. In this study, the cyclohexylamine oxidase (CHAO) gene from Acinetobacter sp. YT-02 was cloned. Amino acid sequence alignment indicated that the cyclohexylamine oxidase (CHAO_YT-02) was 48% identical to its homolog from Brevibacterium oxydans IH-35A (CHAO_IH-35). The enzyme was expressed in Escherichia coli BL21 (DE3), and purified to apparent homogeneity by Ni-affinity chromatography. The purified enzyme was proposed to be a dimer of molecular mass of approximately 91 kDa. The enzyme exhibited its maximum activity at 50°C and at pH 7.0. The enzyme was thermolabile as demonstrated by loss of important percentage of its maximal activity after 30 min incubation at 50°C. Metal ions Mg²⁺, Co²⁺, and K⁺ had certain inhibitory effect on the enzyme activity. The kinetic parameters K _m and V _max were 0.25 ± 0.02 mM and 4.3 ± 0.083 μM min^-1, respectively. The biochemical properties, substrate specificities, and three-dimensional structures of CHAO_YT-02 and CHAO_IH-35 were compared. Our results are helpful to elucidate the mechanism of microbial degradation of CHAM in the strain YT-02. In addition, CHAO_YT-02, as a potential biocatalyst, is promising in controlling CHAM pollution and deracemization of chiral amines.