Production, purification, and properties of thermostable xylanase from Clostridium stercorarium

Abstract

The production of xylanase and endoglucanase in Clostridium stercorarium has been studied in different conditions. Activities were higher when the organism was grown on xylan and cellulose than on soluble substrates. Catabolite repression of xylanase synthesis occurred when glucose and other readily metabolizable substrates were added during growth on cellulose. Three endoxylanases, A, B, and C, from culture filtrate were purified to homogeneity. Most of the properties of xylanases A, B, and C were similar (optimum pH in the range of 5.5–7.0 at 65 °C; isoelectric pH, 4.4–4.5; Km values of 2.9–3.7 mg/mL). The enzymes were inactivated by Hg2+ and p-chloromercuribenzoate but slight inhibition was obtained with more specific thiol reagents such as 5,5′-dithiobis(2-nitrobenzoic acid) and N-ethylmaleimide. Carbohydrate content (3–19%) and half-life (2 min 30 s to 90 min) varied. Patterns of hydrolysis demonstrate that the three enzymes are endo-splitting enzymes able to break down xylan at random giving xylobiose and xylotriose as the main end products. The three enzymes exhibited immunological cross-reactivity.