Glucanases active site

Varghese and coworkers have identified the active site nucleophiles of two crystalline ) -D-glucan endohydrolases from germinating barley [70]. In more recent work, Hej and coworkers were able to introduce 2,3-epoxypropyl- -laminaribioside 8 (n = 1) into the active site of the crystalline l,3-/3-D-glucanase from barley [71]. A subsequent X-ray crystallographic investigation gave invaluable information about the active site of this enzyme and the point of attachment between enzyme and inhibitor was confirmed. 

Common for all eellulose- and stareh-selective glucanases is their substrate-binding active site, which normally contains several subsites (Fig. 33). A subsite is comprised... 

Fig. 33. Schematic representation of the active site of a glucanase comprised of six subsites.

The mechanism of action of glucanases is strongly influenced by the shape and structure of the active site. exo-Enzymes normally have a pocket or a tunnel-shaped active site, which forces the enzyme to attack a chain end of the polysaccharide substrate. " The active site of endo-enzymes has the shape of a cleft. e polymeric backbone (provided that the active site can accommodate the sequence of tire polysaccharide). Furthermore, some glucanases also contain a binding domain, which enables reversible sorption onto (and, thus, hydrolysis of) nondissolved polysaccharides, such as granular starch and fibrous cellulose. 

The intestinal surface membrane from rats contains both (1 4)-a- and (1 6)-a-D-glucosidase (-glucanase) activities and these enzymes have been given the trivial names of sucrase and isomaltase , respectively. The concurrent action of the sucrase and isomaltase active sites of the hybrid sucrase-isomaltase enzyme complex has been studied on the hexasaccharide (1). Hydro-... 

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