Enzymatic properties of a neutral endo-1,3(4)-beta-xylanase Xyl II from Bacillus subtilis

A Bacillus sp. CCMI 966, characterised as Bacillus subtilis, has a duplication time of about 24 min. It produces at least two extracellular xylanases, Xyl I and Xyl II. The extracellular xylanase activity seems to be strongly correlated with the biomass growth profile. The Xyl II isoenzyme was purified by ammonium sulphate precipitation and anionic exchange chromatography, with a purification factor of 8.3. The molecular weight of the isoenzyme was estimated by SDS-PAGE revealing that Xyl II is a multimeric enzyme with a catalytic subunit of about 20 kDa. Under non-denaturing conditions, a molecular weight of about 340 kDa was obtained by native PAGE gel and of 20 kDa by gel filtration chromatography. The enzyme showed an optimum pH and temperature of 6.0 at 60 degrees C. Xyl II was stable at 40 degrees C for 180 min at pH 6.0. The specificity of Xyl II for different substrates was evaluated. Xyl II presents a higher affinity towards OSX, with a K(m) of 1.56 g l(-1) and showed the ability to hydrolyse laminarin, with a K(m) of 1.02 g l(-1). Xylotetraose is the main product of xylan degradation. The Xyl II ability for binding to cellulose and/or xylan was also studied.