Page 192 - Advances in Textile Biotechnology

Enzymatic treatment of wool and silk fi bres 173

Table 8.1 The Enzyme Commission’s system of classification of peptidases
(NC-IUBMB, 2008)
Sub-subclass Type of peptidase Number of entries
3.4.11 Aminopeptidases 20
3.4.13 Dipeptidases 12
3.4.14 Dipeptidyl-peptidases and tripeptidyl- 9
peptidases
3.4.15 Peptidyl-dipeptidases 4
3.4.16 Serine-type carboxypeptidases 4
3.4.17 Metallocarboxypeptidases 20
3.4.18 Cysteine-type carboxypeptidases 1
3.4.19 Omega peptidases 9
3.4.21 Serine endopeptidases 98
3.4.22 Cysteine endopeptidases 54
3.4.23 Aspartic endopeptidases 38
3.4.24 Metalloendopeptidases 80
3.4.25 Threonine endopeptidase 1

Four distinct families are the serine endopeptidases (such as chymotryp-
sin, trypsin and subtilisin), the cysteine endopeptidases (such as papain), the
aspartic endopeptidases (such as pepsin) and the metalloendopeptidases
(such as thermolysin). In particular, serine endopeptidases have been exten-
sively studied.
Within Group 3, hydrolases, other enzymes such as lipases and cutinases

have been used in the treatment of wool fibres to try to remove surface
lipid from wool to improve the wettability of the fibres and improve sub-

sequent dyeing and finishing. Both lipase and cutinase belong to the ester

hydrolases (EC 3.1.X.X) enzyme class, which are capable of catalysing the
hydrolysis of ester bonds. Lipases (triacylglycerol lipase EC 3.1.1.3) catalyze
the hydrolysis of lipid esters. Cutinases (EC 3.1.1.74) hydrolyze cutin, the
wax-like, amorphous biopolyester in the outermost layer of higher plants,
composed of hydroxyl and epoxy fatty acids, and predominantly, esters.
Cutinases are specific for primary alcohol esters (Liu et al., 2008). They have

been used in order to remove the lipid layer from the wool surface, result-
ing in more efficient subsequent enzymatic treatment with proteases.

There is increasing interest in use of the protein-crosslinking enzymes
transglutaminases (EC 2.3.1.13) for surface modification of wool fi bres.

Transglutaminases belong to the class of transferases and act by a different
mechanism from hydrolases. These enzymes can catalyse the post-
translational modification of proteins by the formation of isopeptide bonds.

This occurs either through protein cross-linking via ε-(γ-glutamyl)lysine
bonds or through incorporation of primary amines at selected peptide-
bound glutamine residues (Griffi n et al., 2002a). This crosslinking leads to

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