The involvement of phosphorylated serines in calcium-binding crustaceans proteins has been claimed both in the case of CAP-1 (calcification-associated peptide), isolated from the exoskeleton of Procambarus clarkii, and in orchestin (32, 33) and may be involved in GAP 65 as well. Furthermore, although its primary function is the conversion of chitin into chitosan, the role of the polysaccharide deacetylase domain in GAP 65 function is not known.