Page 244 - Advances in Textile Biotechnology

Functionalisation of wool and silk fi bres using enzymes 225

often been claimed, but it has never been directly proved by determination
of the newly formed ε-(γ-glutamyl)lysine bonds. Tensile measurements have
always been used as an indirect method to assess crosslinking. However,

single-fibre measurements have never been reported. This does not mean
that TGase-catalysed crosslinking did not occur within wool fi bres, but it is

very difficult to understand to what extent the observed changes in fi bre
strength were the result of crosslinking alone or if other unknown experi-
mental factors played some role.
To overcome some limitations imposed by the accessibility of amino acid
residues and to effectively functionalise protein fibres, TGase and tyrosi-

nase can be used in combination with suitable freely diffusible small molec-
ular weight compounds able to take part in the reaction. Various primary
amine reagents and a wide range of phenolic compounds are TGase and
tyrosinase substrates, respectively. These compounds covalently bound to

the surface or in the bulk of protein fibres by enzyme-mediated reaction
will impart on silk or wool the specific functionality carried by their pendant

group. Another approach would be the preliminary induction of suitable
changes in surface chemistry by plasma or electron beam irradiation or
grafting treatments in order to increase the number of potentially reactive
sites available for subsequent enzymatic functionalisation. The combination
of emerging nano- and biotechnologies represents an attractive fi eld of
intensive research likely to bring real innovation in textile processing in the
near future.
With reference to the different sources of TGase and tyrosinase enzymes,
a careful screening and selection of the enzymatic activities better fi tting
the needs of the intended application is an important prerequisite for the
success of any laboratory-scale or pilot trial. The possible interference of
additives or contaminants (especially the presence of other enzyme activi-

ties) must be firstly evaluated. More importantly, enzymes must be selected
with a special attention to their intrinsic properties and performance, as it
has been shown that different sources of the same enzyme, such as the
tyrosinases from T. reesei and from A. bisporus, display radically different
properties in terms of reaction kinetics and substrate specifi city.
Finally, one of the most critical issues for the industrial exploitation of
enzymes is their mass production and supply at a reasonable price. In recent
years, TGases and tyrosinases have attracted much interest from scientists
and technologists from various sectors, including textiles. Despite the high
attractiveness of enzymatic functionalisation and crosslinking of protein
fibres, the development of large-scale industrial applications is still blocked

because tyrosinase is currently not commercially available in suffi ciently
large quantities and at a reasonable cost to support process scale up, whereas

TGase is commercially available but its formulation does not fit the require-
ments of textile processing. TGases and tyrosinases have demonstrated that

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