Comparative Analysis of the Family 10 and Family 11 Xylanase From Dictyoglomus SPP RT46.B1 on Pine and Eucalypt Kraft Pulps, 1997 Biological Sciences Symposium Proceedings

Dictyoglomus spp Rt46.Bl produces two thermophilic xylanases: a family 10 xylanase (XynA) and a family 11 xylanase (XynB). The Rt46.B 1 XynB family 11 xylanase was able to enhance the bleachability of pine kraft oxygen pulp to ECF bleaching (DED) and eucalypt kraft oxygen pulp to both ECF bleaching and TCF bleaching (Q[PO]), however, the Rt46.Bl XynA family 10 xylanase had little or no effect on final brightness of pine and eucalypt kraft oxygen pulps following ECF bleaching, even under very high enzyme loading (> 50XU/g pulp). XynA and XynB showed differences in their activities on the fibre-bound kraft pulp xylans, consistent with these differences in the efficacy of the XynA and XynB pretreatment on the final pulp brightness. Measured on oat spelts xylan, the apparent specific activity of XynB was at least 40-fold higher than that of XynA. At enzyme dosages of 10XU/g pulp, XynA released mostly xylose and xylobiose following extended incubation with pine kraft pulp, whereas XynB released xylobiose and xylotriose in addition to a range of higher molecular weight hydrolysis products. Additionally, XynA and XynB produced more or less identical amounts of reducing sugars from pine and eucalypt kraft oxygen pulps. However, XynB released almost twice the number of chromophoric materials from the pulps (as measured by absorbance of the hydrolysate at 280nm). Finally, the binding patterns of XynA and XynB to the kraft pulps were different in terms of the degree of pulp binding by XynA and XynB with respect to solution pH. 1 XU of XynA bound tightly to O.lg pulp at low pH (pH6.0, 12.5mM sodium acetate buffer), but remained mostly unbound at high pH (pH10.0, 12.5mM CAPS buffer). In contrast, XynB remained mostly bound to the pulp at all pH values tested (6.0, 8.0 and 10.0). The presence of salt appeared to enhance the binding of both XynA and XynB to kraft pulp.