A comparative study on depolymerization of chitosan by proteolytic enzymes

Proteolytic enzymes such as pepsin, papain and pronase caused depolymerization of chitosan, a co-polysaccharide of glucosamine and N-acetyl glucosamine residues linked by β-1,4-glycosidic bonds. The pH optima of these enzymes towards chitosanolysis were different from that towards their own substrates, indicating the involvement of pH-sensitive conformational changes during specific and non-specific activities. The depolymerization reaction obeyed Michaelis-Menten kinetics and Km and Vmax values indicated higher affinity of pepsin towards chitosan. The chitosanolytic products were low molecular weight chitosans (LMWC, a major product), chitooligomers (COs) as well as monomers. Low molecular weight chitosans had molecular weight in the range, 4.1–10.0 kDa depending on the reaction time. FT-IR indicated a decrease in the degree of acetylation of LMWC. GPC and HPLC of COs showed a degree of polymerization of 2–8 with a preponderance of di- to hexamer including monomers.