Purification and characterization of a pyruvated-mannose-specific xanthan lyase from heat-stable, salt-tolerant bacteria

Abstract

A xanthanase complex secreted by a consortium of heat-stable, salt-tolerant bacteria includes a lyase that specifically removes terminal pyruvated β-D-mannose residues from the side chains of xanthan gum. The enzyme was purified to homogeneity from the culture broth following ion-exchange chromatography and gel permeation chromatography. It consists of a single subunit of molecular weight 33,000. The enzyme is stable to 55°C for more than 6 h in 20 mM sodium phosphate buffer (pH 5.0) containing 0.25 M NaCl. Optimal enzyme activity was observed at 0.05 M NaCl and a pH of 5. The enzyme has a pI of 3.7. It does not remove unsubstituted terminal β-D-mannose residues from xanthan side chains nor does it hydrolyze p-nitrophenyl-β-D-mannose. Treatment of xanthan with purified lyase results in a polysaccharide containing side chains terminating in an unsaturated 4,5-ene-glucuronic acid.