What is the pattern of acetylation?

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The pattern of acetylation (abbreviated as PA) describes the distribution of N-acetylglucosamine and glucosamine units within a chitosan molecule. As all chitosans available commercially today are produced using chemical protocols, either by partial de-N-acetylation of chitin or by partial re-N-acetylation of polyglucosamine, they are invariably characterized by a random pattern of acetylation. However, the pattern of acetylation of naturally occurring chitosans which are produced from chitin through the action of enzymes called chitin de-N-acetylases is unknown at present. Theoretical considerations suggest that the pattern of acetylation will have a deep influence on the bioactivity of chitosans, at least if a sequence-specific chitosan hydrolase is present in the target tissue. However, in the absence of chitosans with non-random patterns of acetylation, this hypothesis cannot (yet) be verified experimentally. However interestingly, according to some definitions, chitosans are co-polymers of randomly distributed N-acetylglucosamine and glucosamine residues in different ratios. According to this definition, chitosans with non-random patterns of acetylation would not even fall under the term chitosan.