DeproteinatedA. niger biomass contains several covalently bound amino acids. The most abundant are arginine, serine, and proline in molar ratio of 3:2:2. One order of magnitude less is the amount of valine, phenylalanine, leucine and glycine. On deacetylation and separation of chitosan from glucan, the main three amino acids remain bound predominantly to chitosan, whereas the hydrophobic amino acids accompany mainly glucan. The presence of arginine could be the cause of stronger basicity of fungal chitosan compared to polyglucosamine.