Characterization of Hexenuronosyl Xylan-degrading Enzymes Produced by Paenibacillus sp. 07

The enzyme involved in hexenuronic acid (HexA) removal from kraft pulp was identified in Paenibacillus sp. strain 07. Extracellular and intracellular enzymes of Paenibacillus sp. were assessed for their hexenuronosylxylotriose (∆X3) degradation activity. First, ∆X3 was obtained from hardwood kraft pulp by enzymatic hydrolysis using three commercial enzymes. Crude extracellular and intracellular enzyme fractions were obtained from Paenibacillus cultures cultivated in 0.5% (w/v) birch wood xylan as the sole carbon source. The ∆X3-degrading activities of the enzyme fractions were measured by hydrolysis assays in sodium acetate buffer containing ∆X3 substrate (pH 6) at 50 °C. The reaction products were analyzed by high-performance anion-exchange chromatography with pulsed amperometric detection. The enzyme fractions displayed different chromatogram patterns. After treatment with the intracellular enzyme fraction, the chromatograms displayed xylose and hexenuronosyl xylobiose (∆X2) peaks. The chromatogram patterns of the extracellular fraction assays indicated xylose, xylotriose, and ∆X2 production. Thus, the intracellular enzymes of Paenibacillus can hydrolyze the xylosidic linkages at the reducing ends of ∆X3, whereas a specific extracellular enzyme can hydrolyze HexA. This enzyme is potentially applicable to HexA removal during bio-bleaching.