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88 Advances in textile biotechnology

L182A

N84A

V184A L81A

H188 OX

L189A

PA 6.6 model
substrate-Tl

4.3 Detail of the active site x-ray structure of cutinase with the energy
minimized structure of the tetrahedral intermediate (TI) PA 6.6 model
substrate. The catalytic histidine (H188) and oxyanion-hole (OX) are
shown. Residues mutated in this study are labelled as: L81A, N84A,
L182A, V184A and L189A (Araújo et al., 2007).

In addition to hydrolytic enzymes, oxidases from lignolytic fungi have
been shown to depolymerize polyamides. Some studies demonstrated that
manganese peroxidase was able to modify the surface of PA 6.6 and PA 6

without reducing the fibre diameter (Friedrich et al., 2007; Klun et al., 2003).
Nylon-degrading peroxidases attack methylene groups adjacent to the
nitrogen atoms and the reaction then proceeds in an auto-oxidative manner
(Deguchi et al., 1997, 1998).
Fujisawa et al. (2001) have investigated a laccase-mediator system for its
ability to degrade polyamide 6.6. Using 1-hydroxybenzotriazole (HBT) as
a laccase mediator, they have shown that PA 6.6 membranes are disinte-
grated after 2 days of treatment. Other investigations where a laccase-
mediator system was used to increase the hydrophilicity of PA 6.6 have
shown that the rising height as a parameter for hydrophilicity was enhanced
from 1.8 (untreated) to 3.8 cm after a 300 s treatment with laccase and
violuric acid as mediator, and to 5.5 cm with laccase alone (Miettinen-
Oinonen et al., 2002, 2004). Despite all the developments in this area, the
degradation of polyamide with oxidative enzymes seems to be diffi cult to

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