Xanthine oxidase of Acinetobacter calcoaceticus RL2-M4: Production, purification and characterization

Xanthine oxidase (EC 1.17.3.2) is a key enzyme of purine metabolism and has potential applications in food and pharmaceutical industries. In the present study, a new bacterial source of xanthine oxidase i.e. Acinetobacter calcoaceticus RL2-M4 with high oxidase activity was isolated from soil. The culture conditions were optimized with one variable at a time (OVAT) and response surface methodology (RSM) approaches included: a minimal salt medium (MSM) of pH 7.0 supplemented with 0.8% yeast extract, 8.5 mM xanthine and incubation at 30 °C for 24 h. Under these culture conditions 11.57 fold increase in the production of this enzyme was achieved. The enzyme was purified from A. calcoaceticus RL2-M4 using anion exchange chromatography to 8.18 fold with 31% yield and specific activity of 4.58 U/mg protein. SDS-PAGE analysis of the purified enzyme revealed that it was homodimer of 95 kDa and its native molecular mass was estimated to be 190 kDa. This enzyme was found to be stable at 35 °C for 5 h. The purified xanthine oxidase of A. calcoaceticus RL2-M4 had K_m 0.3 mM and V_max 5.8 U/mg protein using xanthine as substrate. The activity and stability characteristic of xanthine oxidase of A. calcoaceticus RL2-M4 makes it a potentially good enzyme for industrial applications.