Mechanism of the inhibition of milk xanthine oxidase activity by metal ions: a transient kinetic study

Association between serum copper levels and prevalence of hyperuricemia: a cross-sectional study

Hyperuricemia has been recognized as a worldwide public health concern. This study was conducted to examine the association between serum copper (Cu) concentration and the prevalence of hyperuricemia in a middle-aged and elderly population. Serum Cu concentration was measured by Roche modular P800 using the PAESA method. Serum uric acid (UA) concentration was detected by a Beckman Coulter AU 5800. Presence of hyperuricemia was defined as serum UA ≥ 416 μmol/L for men and ≥360 μmol/L for women. The association between serum Cu concentration and the prevalence of hyperuricemia was evaluated by logistic regression. The prevalence of hyperuricemia was 17.6% (n = 6,212) in the present study. Relative to the lowest quintile, the age- and sex-adjusted odds ratios for hyperuricemia were 1.38 (95% CI: 1.12 to 1.70), 1.34 (95% CI: 1.07 to 1.66), and 1.53 (95% CI: 1.23 to 1.91) in the third, fourth, and fifth serum Cu concentration quintiles (P for trend < 0.001). Similar results were found both in men and women subgroups. None of the findings were materially altered after adjustment for additional potential confounders. In conclusion, in this population-based cross-sectional study, serum Cu concentration was positively associated with the prevalence of hyperuricemia.

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.

Thermostable Xanthine Oxidase Activity from Bacillus pumilus RL-2d Isolated from Manikaran Thermal Spring: Production and Characterization

Xanthine oxidase is an important enzyme of purine metabolism that catalyzes the hydroxylation of hypoxanthine to xanthine and then xanthine to uric acid. A thermostable xanthine oxidase is being reported from a thermophilic organism RL-2d isolated from the Manikaran (Kullu) hot spring of Himachal Pradesh (India). Based on the morphology, physiological tests, and 16S rDNA gene sequence, RL-2d was identified as Bacillus pumilus. Optimization of physiochemical parameters resulted into 4.1-fold increase in the xanthine oxidase activity from 0.051 U/mg dcw (dry cell weight) to 0.209 U/mg dcw. The xanthine oxidase of B. pumilus RL-2d has exhibited very good thermostability and its t1/2 at 70 and 80 °C were 5 and 1 h, respectively. Activity of this enzyme was strongly inhibited by Hg(2+), Ag(+) and allopurinol. The investigation showed that B. pumilus RL-2d exhibited highest xanthine oxidase activity and remarkable thermostability among the other xanthine oxidases reported so far.

Interaction of Cu2+ ion with milk xanthine oxidase

The interaction of Cu2+ ion with milk xanthine oxidase (XO) has been studied by optical spectroscopy, circular dichroism, ESR and transient kinetic techniques. It is observed that XO forms optically observable complexes with Cu2+ ion. The pH dependence studies of the formation of Cu2+-XO complex by optical spectroscopy and circular dichroism show that at least one ionizable group may be responsible for the formation of the complex. The EPR studies show that Cu2+ ion binds to XO with sulfur and nitrogenous ligands. The transient kinetic study of the interaction of Cu2+ with XO shows the existence of two Cu2+ bound XO complexes formed at two different time scales of the interaction, one at < or =5 ms and the other one at around 20 s. The complex formed at longer time scale may be responsible for the inhibition of the enzyme activity.