Page 191 - Advances in Textile Biotechnology

172 Advances in textile biotechnology

especially for wool shrink-resistance, and simultaneously to improve dye-
ability, handle and whiteness of wool are well recognised.
Silk has excellent properties. Apart from uses in textiles, in recent years

there has been increasing interest in the application of silk fibroin to the
development of various biotechnological uses and biomedical devices. The
structure of silk protein has therefore been extensively investigated through
amino acids sequencing and other studies. Biotechnology has been used in
the processing of raw silk: for example enzymatic degumming to produce

lustrous silk fibres for textile uses and also for the extraction of silk proteins,

especially highly crystalline fibroin protein for medical uses.
Enzymatic treatments of protein fibres have been extensively investi-

gated with the focus on wool and silk. This chapter provides information
on the major enzymes used for protein fi bre processes and a brief explain-
ation of the protein structure of wool and silk fi bres. Recent developments
in the application of enzymes in wool scouring and fi nishing processes to
achieve a variety of effects including softness, reduction of prickle and
shrink-resistance are reviewed. The review also includes recent develop-
ments in the application of enzymes in silk degumming and fi nishing.

8.2 Enzymes used for processing of protein fi bres

Enzymes are biological catalysts for specific chemical reactions and they
require comparatively mild conditions. All enzymes are proteins and bio-

degradable. The precise reaction specificity of an enzyme can be used for
specific or targeted textile finishing without causing undesirable effects.

Enzymes are classified by the Enzyme Commission of the International

Union of Biochemistry into six groups: oxidoreductases; transferases;
hydrolases; lyases; isomerases and ligases. Most enzymes used in the textile
industry belong to Group 3, hydrolases, and this group includes the amy-
lases, cellulases, pectinases, catalyses and proteases that are used for various
textile applications such as desizing, bioscouring, bio-polishing, bleach
clean-up and imparting wool shrink-resistance. Proteases, proteolytic
enzymes or peptidases are general terms for enzymes that catalyse the
hydrolysis of certain peptide bonds in protein molecules (forming the group
EC 3.4.X.X of hydrolases). These have been suggested for use in wool

processing to improve scouring efficiency, and handle properties, and to
impart shrink-resistance and low temperature dyeability. Proteases are also
used for silk degumming processes.
Proteolytic enzymes can be divided into exopeptidases (which hydrolyse
terminal peptide bonds) and endopeptidases (which hydrolyse peptide
bonds inside the substrate molecule). Proteolytic enzymes can be further
grouped according to the chemical nature of the catalytic site. They are
divided between 13 sub-subclasses (Table 8.1).

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