The enzyme, originally characterized from the thermophilic anaerobic bacterium Thermoanaerobacter sp. X514, catalyses a reversible reaction. In the synthetic direction it produces oligosaccharides with a degree of polymerization (DP) of 3, 4 and 5. The phosphorolysis reaction proceeds to completion, although activity is highest when the substrate has at least three residues. cf. EC 2.4.1.339, ¦Â-1,2-mannobiose phosphorylase.