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Functionalisation of wool and silk fi bres using enzymes 197

mobaraensis has been achieved at low costs (Yokoyama et al., 2004). This
TGase is commercialised by Ajinomoto under the Activa® brand name for

food processing, and finds application at industrial scale for improving the

texture of meat and fish or dairy products. The S. mobaraensis TGase is a
secreted protein activated outside the cytoplasm, which participates in
mycelial growth and has a role in morphological differentiation. Unlike
many tissue TGases, it has a relatively low molecular weight (37 842 Da,
based on its known primary structure). The isoelectric point is 9, the
optimum pH for enzymatic activity is in the range 5–8, and the optimum
2+
temperature is 55 °C. The Ca -independency offers several advantages
when biotechnological applications are sought. With respect to substrate
specificity, the TGase from S. mobaraensis has the ability to crosslink most

food proteins, such as legume globulins, wheat glutens, egg yolk and albumin

proteins, actins, myosins, fibrins, milk caseins, α-lactalbumin, and
β-lactoglobulin as efficiently as mammal TGases by formation of ε-(γ-

glutamyl)lysine bonds. Protein solutions, such as soybean, milk, beef, and

pork proteins, chicken and fish gelatine and myosins can be gelled. In a
series of recent publications Lantto et al. (2005a, 2006, 2007a) reported
results on the effect of S. mobaraensis TGase on the thermal, gel forming,
textural, and water-holding properties of various meat systems, which
further support the utility of this enzyme as a biotechnological food pro-
cessing tool.
In a recent study Kulik et al. (2009) investigated the reactivity of synthetic
substitutes for Lys and Gln as substrates of microbial TGase from S. mob-
araensis. The reactivity of ω-amino acids used as Lys substitutes increased
with increasing the hydrocarbon chain length from C 5 to C 7 . The conversion
reached about 70% with 7-aminoheptanoic acid as substrate. With refer-
ence to Gln substitutes, high reactivity and conversion levels were achieved
only with glutaric mono and diamine, i.e. with substrates having a C 5 hydro-
carbon chain similar to the natural Gln substrate. Substrates with longer
hydrocarbon chains (i.e. C 6 , adipic diamine) displayed sensibly lower reac-
tivity, indicating that restrictions for the Gln substitute are stronger than
for the Lys substitute. Kulik et al. also succeeded in demonstrating the fea-

sibility of a completely artificial microbial TGase-catalysed reaction by
producing mono and diadducts of DNS-cadaverine and glutaric diamine,
thus opening new opportunities for surface polymer modification by graft-

ing functional compounds at distinct sites through an environmentally
friendly reaction based on microbial TGase catalysis.

9.2.2 Applications of transglutaminases: advantages
and limitations
Although currently the main application sector of TGase is food processing,
novel potential applications have emerged during the last years. These

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