Tyrosinase polymer modifications

The enzymatic treatment of chitosan in the presence of tyrosinase and phenol derivatives produced new materials based on chitosan.91 During the reaction, unstable o-quinones were formed, followed by the reaction with the amino group of chitosan to give the modified chitosan. The tyrosinase-catalyzed modification of chitosan with phenols dramatically altered rheological and surface properties of chitosan. The modification with chlorogenic acid onto chitosan conferred the water solubility of chitosan under basic conditions.92 A new water-resistant adhesive was developed by the tyrosinase-catalyzed reaction of 3,4-dihydroxyphenethylamine and chitosan.93 Poly(4-hydroxystyrene) was modified with aniline by using tyrosinase catalyst.94 The incorporated ratio of aniline into the polymer was very low (1.3%). 

In living cells, various oxidoreductases play an important role in maintaining the metabolism of living systems. So far, peroxidase containing Fe-active site, laccase containing Cu-active site, tyrosinase (polyphenol oxidase, Cu-active site), bilirubin oxidase (Cu-active site), etc, have been reported to act as catalyst for oxidative polymerization of phenol and aniline derivatives and for polymer modification via oxidative coupling. 

Tyrosinase (polyphenol oxidase, a copper-containing monooxygenation enzyme) was used as catalyst for the modification of natural polymers. Phenol moiety-incorporated chitosan derivatives were subjected to tyrosinase-catalyzed cross-linking, yielding stable and self-sustaining gels.90 Tyrosinase also catalyzed the hybrid production between the modified chitosan and proteins. 

The first two steps in the synthesis of melanin are catalyzed by tyrosinase, a copper-containing oxidase, which converts tyrosine to dopaquinone. All subsequent reactions presumably occur through nonenzymatic auto-oxidation, in the presence of zinc, with formation of the black to brown pigment eumelanin. The yellow to reddish brown, high-molecular-weight polymer known as pheomelanin and the low-molecular-weight trichromes result from addition of cysteine to dopaquinone and further modification of the products. Pheome-lanins and trichromes are primarily present in hair and feathers. 

Moreover, tyrosinase-catalyzed activity is not limited only to protein substrates. Burke et al. have focused their work on the modification of biocompatible polymers such as poly(ethylene glycol) with DOPA in an effort to impart adhesive qualities to the polymers for biomedical application. Although PEG itself is not adhesive, it represents a candidate budding block for a synthetic tissue adhesive because of its high water solubility, low immunogenicity and toxicity, and availability of end groups easily modifiable with amino acids and peptides [61]. Burke et al. [12] synthesized several linear and branched PEG molecules with end groups modified by DOPA residues and have characterized their oxidation-induced... 

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