Accepted name: xyloglucan-specific exo-β-1,4-glucanase
Reaction: Hydrolysis of (1→4)-D-glucosidic linkages in xyloglucans so as to successively remove oligosaccharides from the chain end.
Other name(s): Cel74A
Systematic name: [(1→6)-α-D-xylo]-(1→4)-β-D-glucan exo-glucohydrolase
Comments: The enzyme removes XXXG heptasaccharides, XXLG/XLXG octasaccharides and XLLG nonasaccharides from the end of tamarind seed xyloglucan polymers in a processive manner. Hydrolysis occurs at the unsubstituted D-glucopyranose residue in the main backbone. It is not known whether the cleavage takes place at the reducing or non-reducing end of the polymer. Very low activity with β-D-glucans. The enzyme from Chrysosporium lucknowense shifts to an endoglucanase mode when acting on linear substrates without bulky substituents on the polymeric backbone such as barley β-glucan.
1.  Grishutin, S.G., Gusakov, A.V., Markov, A.V., Ustinov, B.B., Semenova, M.V. and Sinitsyn, A.P. Specific xyloglucanases as a new class of polysaccharide-degrading enzymes. Biochim. Biophys. Acta 1674 (2004) 268–281. [PMID: 15541296]
[EC created 2005, withdrawn at public-review stage, modified and reinstated 2006, modified 2011]

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