Transfer reactions catalysed by a fungal β-D-xylosidase: enzymic synthesis of phenyl β-D-xylobioside

Xylanolytic enzymes from fungi and bacteria

The development of new analytical techniques and the commercial availability of new substrates have led to the purification and characterization of a large number of xylan-degrading enzymes. Furthermore, the introduction of recombinant DNA technology has resulted in the selection of xylanolytic enzymes that are more suitable for industrial applications. For a successful integration of xylanases in industrial processes, a detailed understanding of the mechanism of enzyme action is, however, required. This review gives an overview of various xylanolytic enzyme systems from bacteria and fungi that have been described recently in more detail.

Specificity mapping of cellulolytic enzymes: classification into families of structurally related proteins confirmed by biochemical analysis

The specificities of 15 cellulolytic enzymes have been examined using chromophoric glycosides derived from D-glucose, cellobiose, higher cellooligosaccharides, lactose, D-xylose, and beta-(1,4)-xylobiose. Coinciding with a classification based on hydrophobic cluster analysis of amino acid sequences, six families each showing a characteristic specificity pattern were observed. Furthermore, in these cases where the anomeric forms of reaction products were determined, results seem to indicate conservation of intrinsic reaction mechanism (single or double displacement) within each family. On the other hand, the low molecular weight substrates do not discriminate exo- from endocellulases. This functional differentiation is speculated to originate from the presence, in exoenzymes, of a tunnel-shaped active site formed by extra loops in their structure.