## 2 Experimental Section
### Enzyme Characterization
Because only xylooligosaccharides containing six or fewer xylose units could be detected with the selected chromatographic parameters, we postulated that the products with a higher degree of polymerization (DP) could not be identified by the absence of xylooligomer patterns with longer retention times. With regard to the highest hydrolysis percentage obtained with the DNS method, we hypothesize that the identification of the hydrolysis products by their retention times results in greater specificity. Conversely, the detection of reducing sugars by the DNS method, even using xylose as reference, would not distinguish between the reducing ends of the xylose or more complex xylooligomers. Indeed, the effect of transglycosylation could explain the constant rate of hydrolysis obtained by the DNS method after 12 h of incubation (Table 5). As reported by [PERSON] and [PERSON] [47], the transfer of glycosyl groups is a well-known activity of glycosases and glycanes. Consistent with the findings of these authors, the enzyme acts on oligosaccharides or aryl glycosides (e.g., invertase, \(\beta\)-galactosidase, _A. niger_\(\beta\)-glucosidase) to catalyze the formation of various positional isomers of the oligosaccharides. These positional isomers retain the configuration of the glycosidic linkage without specificity for the saccharide acceptor molecule and one particular linkage. For endo-acting glycanes, such as lysozyme, \(\alpha\)-amylases and cellulases, the specificity is evident, and the same type of glycosidic linkage in the saccharide acceptors is formed from the oligosaccharidesadronics that were cleaved previously. In addition, the xylanase produced by \begin{table}
\begin{tabular}{c c c c c} \hline  & \multicolumn{2}{c}{**Soluble**} & \multicolumn{2}{c}{**Insoluble**} \\ \cline{2-5}  & **Specific reducing** & **Hydrolysis (\%)** & **Specific reducing** & **Hydrolysis** \\
**Hydrolysis time (h)** & **sugar (mg) *** & & **sugar (mg) *** & **(\%)** \\ \hline
0 & \(0.000\pm 0.000\) & 0.00 & \(0.031\pm 0.006\) & 1.55 \\
6 & \(0.434\pm 0.011\) & 21.72 & \(0.209\pm 0.036\) & 10.47 \\
12 & \(0.667\pm 0.029\) & 33.35 & \(0.351\pm 0.057\) & 17.54 \\
18 & \(0.554\pm 0.025\) & 27.69 & \(0.345\pm 0.039\) & 17.23 \\
24 & \(0.554\pm 0.025\) & 27.70 & \(0.350\pm 0.037\) & 17.50 \\ \hline Reaction mixtures (final volume of 0.3 mL) containing \% purified Xyl-O1 (6.0 mg\(\cdot\)mL\({}^{-1}\)) and \% substrate solution with soluble or insoluble birchwood xylans (10 mg\(\cdot\)mL\({}^{-1}\)) were incubated at 28 \({}^{\circ}\)C with agitation at 120 rpm. * The amount of the reducing sugar released was estimated by the DNS method. & \\ \end{tabular}
\end{table} 
Table 5: Hydrolysis of soluble or insoluble birchwood xylan catalyzed by purified Xyl-O1. _Anoxyobacillus flavithermus_ BC [48] catalyzes this transglycosylation activity. In other studies, endo-1,4-\(\beta\)-xylanases and \(\beta\)-xylosidases have been used for the synthesis of specific oligosaccharides [49, 50] to obtain a cellulose-xylan polymer hybrid [51]. Our results suggest that the transglycosylation reaction catalyzed by Xyl-O1 can occur after a period of effective hydrolysis, in this case, after a 12 h incubation at 28 \({}^{\circ}\)C. However, specific testing of the transglycosylation reaction is required to confirm this hypothesis of Xyl-O1-promoted catalysis. Table 6 shows the general profile of hydrolysis over the 6.0-24 h incubation period, confirming the predominance of X2 because of the action of Xyl-O1 on the soluble and insoluble fractions of the substrate. For the insoluble and soluble fractions, Xyl-O1 showed a hydrolysis profile with a more relaxed specificity, allowing for the quantification of the products X1 to X6 within six hours of incubation. During this incubation period, xylobiose was the main hydrolysis product released through the activity of the enzyme (Table 6).