Mannan endo-1,4-ò-mannosidase (, endo-1,4-ò-mannanase, endo-ò-1,4-mannase, ò-mannanase B, ò-1, 4-mannan 4-mannanohydrolase, endo-ò-mannanase, ò-D-mannanase, 1,4-ò-<small>D</small>-mannan mannanohydrolase) is an enzyme with systematic name 4-ò-<small>D</small>-mannan mannanohydrolase. It catalyses the hydrolysis of (1âÂÂ4)-ò-<small>D</small>-mannosidic linkages in mannans, galactomannans and glucomannans. The cleavage occurs at random internal sites within the chain, as denoted by the prefix "endo".