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An alkaline ß-mannanase was purified to homogeneity from a culture broth of alkaliphilicBacillussp. N16-5. The enzyme had optimum activity at pH 9.5 and 70°C. It was composed of a single polypeptide chain with a molecular weight of 55 kDa deduced from SDS-PAGE, and its isoelectric point was around pH 4.3. The enzyme efficiently hydrolyzed galactomannan and glucomannan, producing a series of oligosaccharides and monosaccharides. The ß-mannanase gene (manA) contained an open reading frame (ORF) of 1,479 bp, encoding a 32-amino acids signal peptide, and a mature protein of 461 amino acids, with a calculated molecular mass of 50,743 Da. Strain N16-5 ManA, deduced from themanAORF, exhibited relatively high amino acid similarity to the members of the glycosyl hydrolase family 5. The eight conserved active-site amino acids in family 5 glycosyl hydrolase were found in the deduced amino acid sequence of strain N16-5 ManA. [ABSTRACT FROM AUTHOR]