Hydrolyzes the N-acetamido groups of N-acetyl-D-glucosamine polymers in chitin to form chitosan and acetate. [(1->4)-N-acetyl-beta-D-glucosaminyl](n) + n H2O = n acetate + chitosan Evidence supports a metal cofactor but evidence for cobalt is inconsistent. Inhibited by metal chelator ethylenediaminetetraacetic acid (EDTA). kcat is 7 sec(-1) with GlcNAc(5) as substrate. Optimum pH is 8. Optimum temperature is 50 degrees Celsius. Belongs to the polysaccharide deacetylase family.