deacetylase in large quantities in either prokaryotic or eukaryotic host cells for this purpose the dna is inserted into a prokaryotic or eukaryotic expression vector with the appropriate regulatory signals and used to transform cells a variety of appropriate vectors and regulatory signals have been previously developed for this purpose and are well known to those skilled in the art through the use of conventional techniques the deacetylase of this invention can be overexpressed for example in e coli to the extent that they represent a substantial proportion of the total cellular protein the purification of a protein which is expressed at such substantial levels and for which a simple assay system is established is a straightforward matter to one skilled in the art in another aspect the invention relates to methods for converting chitin to chitosan in the claimed methods chitosan is contacted with an enzyme having chitin deacetylase activity the enzyme being produced by recombinant dna techniques in which an isolated dna sequence encoding the enzyme or a biologically active portion thereof is expressed from a dna expression construct the scope of this aspect of the invention includes not only the use of dna characterized by the ability to hybridize to.