Cellulose 1,4-β-cellobiosidase (reducing end)

{{Infobox enzyme

| Name = Cellulose 1,4-β-cellobiosidase (reducing end)

| EC_number = 3.2.1.176

| CAS_number =

| GO_code =

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Cellulose 1,4-β-cellobiosidase (reducing end) ({{EC number|3.2.1.176}}, CelS, CelSS, endoglucanase SS, cellulase SS, cellobiohydrolase CelS, Cel48A) is an enzyme with systematic name 4-beta-D-glucan cellobiohydrolase (reducing end).{{cite journal | vauthors = Barr BK, Hsieh YL, Ganem B, Wilson DB | title = Identification of two functionally different classes of exocellulases | journal = Biochemistry | volume = 35 | issue = 2 | pages = 586–92 | date = January 1996 | pmid = 8555231 | doi = 10.1021/bi9520388 }}{{cite journal | vauthors = Saharay M, Guo H, Smith JC | title = Catalytic mechanism of cellulose degradation by a cellobiohydrolase, CelS | journal = PLOS ONE | volume = 5 | issue = 10 | pages = e12947 | date = October 2010 | pmid = 20967294 | pmc = 2953488 | doi = 10.1371/journal.pone.0012947 | doi-access = free }} This enzyme catalyses the following chemical reaction

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

The CelS enzyme from Clostridium thermocellum is the most abundant subunit of the cellulosome formed by the organism.