IUBMB Enzyme Nomenclature


Accepted name: cellulose 1,4-β-cellobiosidase (reducing end)

Reaction: Hydrolysis of (1→4)-β-D-glucosidic linkages in cellulose and similar substrates, releasing cellobiose from the reducing ends of the chains.

Other name(s): CelS; CelSS; endoglucanase SS; cellulase SS; cellobiohydrolase CelS; Cel48A

Systematic name: 4-β-D-glucan cellobiohydrolase (reducing end)

Comments: Some exocellulases, most of which belong to the glycoside hydrolase family 48 (GH48, formerly known as cellulase family L), act at the reducing ends of cellulose and similar substrates. The CelS enzyme from Clostridium thermocellum is the most abundant subunit of the cellulosome formed by the organism. It liberates cellobiose units from the reducing end by hydrolysis of the glycosidic bond, employing an inverting reaction mechanism [2]. Different from EC, which attacks cellulose from the non-reducing end.

Links to other databases: BRENDA, EXPASY, KEGG, Metacyc, PDB, CAS registry number:


1. Barr, B.K., Hsieh, Y.L., Ganem, B. and Wilson, D.B. Identification of two functionally different classes of exocellulases. Biochemistry 35 (1996) 586-592. [PMID: 8555231]

2. Saharay, M., Guo, H. and Smith, J.C. Catalytic mechanism of cellulose degradation by a cellobiohydrolase, CelS. PLoS One 5 (2010) e1294. [PMID: 20967294]

[EC created 2011]

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