Purification and characterization of thermostable xylose(glucose) isomerase from Bacillus thermoantarcticus

Xylose isomerase produced by Bacillus thermoantarcticus was purified 73-fol d to homogeneity and its biochemical, properties were determined. It was a homotetramer with a native molecular mass of 200 kDa and a: subunit molecul ar mass of 47 kDa, with an isoelectric point at 4.8. The enzyme had a K-m o f 33 mM for xylose and also accepted D-glucose as substrate. Arrhenius plot s of the enzyme activity of xylose isomerase were linear up to a temperatur e of 85 degreesC. Its optimum pH was around 7.0, and it had 80% of its maxi mum activity at pH 6.0. This enzyme required divalent cations for its activ ity and thermal stability. Mn2+, Co2+ or Mg2+ were of comparable efficiency for xylose isomerase reaction, while Mg2+ was necessary for glucose isomer ase reaction.