Fukamizo et al. (26) have determined that the anomeric form of the products obtained from chitosan hydrolysis by chitosanase is an a form indicating that Streptomyces sp. N174 chitosanase is an inverting enzyme.
These data combined with the information obtained from crystalography (38) and site-directed mutagenesis (36) allowed us to conclude that the residue Glu22 acts as a proton donor while the residue Asp40 activates a water molecule which then attacks the C-1 carbon of the sugar residue located at the catalytic site.
Evidence for an inverting mechanism is also sustained by the fact that the two catalytic residues are separated by a distance of 13.8 Å, which is higher than the average of ~10 Å observed in inverting enzymes (40).
The outline of the catalytic mechanism of the chitosanase is shown on the following figure (39):