Purification and characterization of chitin deacetylase from Scopulariopsis brevicaulis

An extracellular chitin deacetylase from Scopulariopsis brevicaulis has been produced using chitin as sole carbon resource of culture medium. The enzyme activity was 10–11 units ml−1 culture supernatant after the strain was shaken at 200 rpm and 29 °C for 96 h. The enzyme was purified 74-fold at 38% yield through ammonium sulfate precipitation, and Sephadex G-25, and G-100 column chromatography. The apparent molecular weight of 55 kDa, as determined by SDS-PAGE and gel filtration chromatography, suggested that the enzyme exists as a single component. The enzyme was active on chitooligosaccharides with at least two N-acetyl-glucosamine residues, but the activity increased with the number of N-acetyl-glucosamine residues. When hexa-N-acetylchitohexaose was used as substrate, the optimum pH for enzyme activity was determined to be 7.5, and the optimum temperature was 55 °C. Under these conditions, the activity of enzyme was studied on water-soluble chitosan, chitin from Aspergillus niger and shrimp crystalline chitin. The structures of products were characterized by FT-IR, XRD and potentiometric titration. The results indicated that degree of substrate crystallinity had an important effect on enzyme activity. The enzyme had high deacetylating activity on amorphous chitin from A. niger mycelium (37% deacylation) and water-soluble chitosan (33%) but low. activity on shrimp crystalline chitin (3.7%).