Page 228 - Advances in Textile Biotechnology

Functionalisation of wool and silk fi bres using enzymes 209

9.4.2 Applications of tyrosinases: advantages and
limitations

Tyrosinases are of great interest for many biotechnological applications in
industry (food processing, textile, pulp and paper industry), medicine (pro-

duction of l-dopa), biosensing (detection and quantification of phenolic
compounds), the environment (removal of phenolic compounds from
wastewater), and for the production of various kinds of proteins and/or
mixed polymer crosslinked networks owing to their ability to oxidise phe-
nolic compounds and to the high reactivity of these primary oxidation
products. However, despite the active research and promising results, com-
mercial tyrosinases suitable for industrial applications are not yet available
on the market.

Production of L-dopa
The ability of tyrosinases to convert monophenols into diphenols can be
exploited for the production of antioxidants with beneficial properties as

food additives or pharmaceutical drugs (Ullrich and Hofrichter, 2007). The
biosynthesis of l-dopa, the preferred drug for treatment of Parkinson’s and
myocardium diseases, has been attempted using Tyr as substrate (Acharya
et al., 2008). The productivity so far achieved by using mushroom tyrosinase
in cell-free systems is still relatively low owing to incomplete conversion of
Tyr and to side reactions leading to formation of dopaquinone, leukodopa-
chrome, and then dopachrome molecules, which spontaneously polymerise
into melanins (de Faria et al., 2007). The use of tyrosinase immobilised in
Cu-alginate gels forming continuous-packed-bed systems allowed increas-

ing productivity, though to a level still not sufficiently high to be competitive
with current chemical processes or with a novel enzymatic process involving
tyrosine phenol-lyase enzyme (Lee et al., 1999).

Biosensing and bioremediation
Enzymes share nanoscale dimensions comparable with those of metal or
semiconductor nanoparticles. This paves the way for the combination of the
unique electronic and photonic properties of nanoparticles with the cata-
lytic functions of biomolecules leading to assembly of novel biosensors,
nanoscale biocircuits, and bioelectronic systems (Willner et al., 2007). The
tyrosinase-stimulated synthesis and growth of gold nanoparticles has been
exploited for developing an optical biosensor applicable to the detection of
tyrosinase activity as a diagnostic system for detecting melanoma cancer
cells and Parkinson’s disease (Baron et al., 2005). The analytical arrays are
relatively rapid and highly sensitive. The tyrosinase-catalysed oxidation of

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