Interaction of Subtilisin-type Protease with Merino Wool Fibres

In order to understand the structural modifications caused by proteolytic enzymes on wool fibers, the interaction of subtilisin-type protease with Merino wool was studied by physical and physico-chemical techniques. Enhanced wool dye affinity and optical microscopy examination indicate increasing fiber damage as a function of enzyme action. Scanning electron microscopy suggests a preferential proteolytic attack on the Cellular Membrane Complex (CMC), a non-cellular and non-keratinic material, while no significant degradation of cortical and cuticular cells was observed. SDS-PAGE (after fiber dissolution in urea) shows progressive proteolysis of low-sulfur containing proteins, which are considered to be part of non-keratinic structures. High ionic strength in the incubation medium provides protection of the fiber interior, by limiting proteolysis to the epicuticule. FTIR-ATR indicates that no change in the redox state of -S-S- cystine bonds takes place, which occurs with currently used oxidative treatments (e.g., Basolan DC). Accordingly, wool top treated with an oxidatively stable serine protease acquires minimal non-felting properties, as proven by the Aachen felting test, even in the presence of hydrogen peroxide. It is concluded that commercially available subtilisin-type proteases are useful tools in the study of wool / enzyme interactions and can be used to enhance hand feel or lustre of wool articles, but might be of limited use in shrink-resistance treatments.