Acetyl xylan esterase-catalyzed deacetylation of chitin and chitosan

Abstract

Acetyl xylan esterase catalyzes the hydrolysis of N-acetyl groups in chitinous materials of variable degrees of polymerization and acetylation. The influence of substrate accessibility is most notable with substrate of high degree of acetylation (DA). The activity rises sharply as the number of acetyl groups in the substrates decreases and at about 24% DA enzyme activity reaches a maximum. Therefore, based on a multiple-attack mechanism we hypothesize that this maximum represents the ideal acetate microstructure for optimal activity of this enzyme. The enzyme partially deacetylates chitin oligomers DP 2–6 with a plateau in deacetylation observed at DP5. These results show that oligomer length is important for enzyme action. By combining successive alkaline and enzymatic deacetylation a process improvement for production of chitosan is suggested.