Purification and characterization of a novel salt-tolerant protease from Aspergillus sp. FC-10, a soy sauce koji mold

Abstract

A novel salt-tolerant protease produced by Aspergillus sp. FC-10 was purified to homogeneity through anionexchange chromatography, preparative isoelectric-focusing electrophoresis, and gel filtration chromatography, with an overall recovery of 12.7%. This protease demonstrated an optimum pH range of 7.0-9.0 for activity, with a stable pH range of 5.0-9.0. The optimum process temperature at pH 7.0 was 65°C. The enzyme has a molecular mass of 28 kDa and was deduced as a monomer with an isoelectric point of 3.75. Enzyme activity was strongly inhibited by 5 mM of HgCl2 and FeCl3, and significantly inhibited by 5 mM of CuSO4, FeSO4, and MnCl2. The activity of this purified protease was inhibited by Na2 EDTA; however, leupeptin, pepstatin A, PMSF, and E-64 did not affect the activity. Based on the N-terminal amino acid sequence and amino acid composition, this purified protease should be classified as a member of the deuterolysin family.