Page 212 - Advances in Textile Biotechnology

9

Functionalisation of wool and silk fi bres using
non-proteolytic enzymes

G. FREDDI, Stazione Sperimentale per la Seta, Italy

Abstract: Wool keratins, silk fibroin and sericin are potential substrates

for various enzymatic reactions and proteases can be used in
environmentally friendly processes for wool antifelting and softening,
and for silk degumming. The use of non-proteolytic enzymes able to
modify the chemistry of amino acid residues without breaking the
peptide bond is reviewed. In particular, transglutaminases and
tyrosinases have the capability to modify the properties of wool and silk

fibres by targeting the reactive side groups of amino acid residues, thus
resulting in activation, functionalisation, and crosslinking.
Key words: wool, keratins, silk, fibroin, sericin, transglutaminase,

tyrosinase.

9.1 Introduction

Wool and silk are protein-based textile fibres widely different in chemical

and physical structure and morphology. Wool has a composite structure
comprising two kinds of cells: cuticle and cortex cells (Zahn et al., 2003).

Coarse fibres may also have a central medulla. Cuticle cells (also called
‘scales’) have a flat shape and overlap each other from root to tip forming

a sheath around the cortex. The cortex forms the bulk of the fi bre and
consists of spindle-shaped interdigitated cells. Cortical cells are held together
by the cell membrane complex (CMC), which also separates cortical cells
from the cuticle. The CMC is a continuous region, containing slightly cross-

linked proteins, that extends throughout the whole fibre. Being the only
continuous phase in the fi bre, it also provides a channel by which dyes and
chemicals can diffuse in and out of wool. Keratin proteins are divided into
four major classes: the low sulfur, the high sulfur, the ultra-high sulfur, and
the high glycine–tyrosine proteins. They widely differ in amino acid com-
position molecular weight, and structure. In particular the content of cystine

(Cys) and the degree of disulfide crosslinking are different.
The raw silk fibres spun by the Bombyx mori silkworm are formed by

two fi broin filaments surrounded by a cementing layer of sericin (Zahn and

Krasowski, 2003). Fibroin and sericin account for about 75 and 25% of the
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