RESUMO
Two thermally stable chitosanase isoforms were purified from the sheaths of chitosan-treated bamboo shoots. Isoforms A and B had molecular masses of 24.5 and 16.4 kDa and isoelectric points of 4.30 and 9.22, respectively. Using chitosan as the substrate, both isoforms functioned optimally between pH 3 and 4, and the optimum temperatures for the activities of isoforms A and B were 70 and 60 °C, respectively. The kinetic parameters K(m) and V(max) for isoform A were 0.539 mg/mL and 0.262 µmol/min/mg, respectively, and for isoform B were 0.183 mg/mL and 0.092 µmol/min/mg, respectively. Chitosans were susceptible to degradation by both enzymes and could be converted to low molecular weight chitosans between 28.2 and 11.7 kDa. Furthermore, the most susceptible chitosan substrates were 50-70 and 40-80% deacetylated for isoforms A and B, respectively. Both enzymes could also degrade chitin substrates with lower efficacy. N-Bromosuccinimide and Woodward's reagent K strongly inhibited both enzymes.
