Production, purification and characterization of two α-amylase isoforms from a newly isolated Aspergillus Oryzae strain S2

A new fungal strain that was isolated from old sweet soy sauce was identified, based on subsequent microscopic studies and analyses of rRNA18S gene sequence, intergenic region rRNA 18S-23S, and aflatoxins production tests, as an Aspergillus oryzae strain. The latter was noted to produce two extracellular α-amylases, namely AmyA and AmyB. The monitoring of alpha-amylase production in the presence and absence of various protease inhibitors indicated that AmyB could be formed from the proteolysis of AmyA. The enzymes were purified to homogeneity through fractional acetone precipitation, size exclusion, and anion exchange chromatography. The molecular masses estimated for AmyA and AmyB by SDS-PAGE were 50 and 42 kDa, respectively. The NH2-terminal of the purified proteins showed the same amino acid sequences. Further biochemical characterization assays revealed that both enzymes attained maximal activity at pH 5.6 and 50 °C. They were activated and stabilized by Ca2+ and were noted to produce maltose and maltotriose as major starch hydrolysis end products. Overall, the findings of the present study indicate that both AmyA and AmyB exhibit a number of promising properties that make them potential strong candidates for application as additives in the bread making industry.

► A new fungal strain identified as Aspergillus oryzae S2, not producing any known aflatoxins, was isolated.
► This strain produces two α-amylases named AmyA and AmyB.
► AmyB is a proteolysis derivative of AmyA.
► Both enzymes attained maximal activity at pH 5.6 and 50 °C and produce maltose and maltotriose as major starch hydrolysis end products.
► These properties make these amylases promising candidates for application as additives in the bread making industry.