Page 227 - Advances in Textile Biotechnology

208 Advances in textile biotechnology

activity has recently become one of the most popular methods in cosmetics.
Tyrosinases are also thought to play a key role in skin diseases like mela-
noma and in the damage of neurons related to Parkinson’s disease (Sato
and Toriyama, 2009). In invertebrates, the tyrosinase-catalysed melanogen-
esis is related to defence reactions and sclerotisation. In plants, tyrosinases
have been suggested to participate in wound healing and defence reactions
mediated by quinones which can create a toxic environment, reduce the
bioavailability of proteins, or contribute to the formation of barriers by
polymerisation reactions. The undesired browning reaction in fruits and
vegetables is related to tyrosinase activity, and methods for controlling it
are constantly being searched in the food industry. In fungi, tyrosinases have
been proposed to participate in spore formation, defence reactions and
pigmentation. In fact, melanogenesis has a role in the formation of repro-
ductive organs and spores and in cell wall protection after physical damage.
All the most recent reports underline the very promising properties of
tyrosinases for biotechnological applications. Fungal tyrosinases appear to
be the most suitable candidates for the establishment of industrial pro-
cesses, because they have been widely used in laboratory studies. Current
limitations to establish commercial sources of tyrosinase enzymes stem
from the fact that native fungal tyrosinases are generally intracellular (with
only few exceptions, such as T. reesei tyrosinase) and are produced in low
quantity, with poorly reproducible biological characteristics. Flurkey et al.
(2008) recently examined the characteristics of various commercial
preparations of mushroom tyrosinase from A. bisporus and found that
they contain variable amounts of other proteins, enzymes (e.g. laccase,
β-glucosidase, cellulase, xylanase), carbohydrates, and phenolic compounds.
Indeed, the presence of contaminants in tyrosinase preparations, if not care-
fully evaluated, might affect the results and their interpretation.
Current problems to be overcome for a wider biotechnological use of
tyrosinases have been outlined by Halaouli et al. (2006) and by de Faria
et al. (2007). One problem is to optimise the production techniques in
mycelial culture, either by submerged culture or solid-state fermentation.
When tyrosinase is produced from the fungal mycelium, it is necessary to
use standardised purification protocols in order to remove the melanin pig-

ments, which often remain bound to the protein after extraction, and other
contaminants. The generally low stability of tyrosinase sometimes hampers
its use and immobilisation techniques have been proposed as a tool to
enhance enzyme stability and to allow repeated use. However, the largest
and still unsolved problem seems to be related to the lack of suitable
expression systems for large-scale heterologous production of tyrosinases,
possibly in the extracellular medium. More research efforts in this direction
are needed to design suitable expression constructs for extracellular pro-
duction and to improve productivity.

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