Purification and characterization of a novel exo-beta-mannanase from Aeromonas sp. F-25

A novel exo-beta-mannanase (1,4-beta-D-mannan mannobiohydrolase) was isolated from the culture fluid of strain No. F-25 of Aeromonas hydrophila subspecies anaerogenes, and purified about 4,000-fold by ammonium sulfate precipitation and successive co.umn chromatographies. The final enzyme preparation appeared to be homogeneous on polyacrylamide gel electrophoresis. The enzyme hydrolyzed the beta-1,4-mannan link in polysaccharides of three or more beta-1,4-linked D-mannose units. The enzyme had a molecular weight of 64,000, pI of 5.9, pH optimum of 6.0, and was stable in a pH region of 5.0 to 8.5 and at temperatures below 45 degrees C. The Km values of the enzyme were 5.1 X 10(-4) M for mannotriose, 2.4 X 10(-4) M for mannotetraose and 1.3 X 10(-4) M for mannopentaose. The enzyme attacked codium and coffee mannans to give only mannobiose. Mannobiosyl- and mannotetraosyl-mannitol were hydrolyzed to produce mannobiose and mannitol, while mannobiose and mannosylmannitol were released from mannotriosylmannitol. The enzyme did not act on mannobiose, p-nitrophenyl-beta-D-mannoside, konjac glucomannan, or guar gum galactomannan. Furthermore, the enzyme catalyzed a transglycosylation reaction.