[Acid-stable and acid-unstable alpha-amylases of the mold fungi Aspergillus].

Acid-sable alpha-amylase of Asp. niger and acid-unstable, alpha-amylase of Asp. oryzae were studied. It was demonstrated, that beside being a more acid-stable properties, alpha-amylase Asp. niger has increased thermal stability as compared to alpha-amylase Asp. oryzae. The molecular weights of acid-stable alpha-amylase and acid-unstable alpha-amylase are 58 000 and 51 000, respectively. The amino acid composition, and the C- and N-terminal amino acids of both forms of alpha-amylases were determined. It was demonstrated, that the enzymes under study contain one sylfhydryl group per mole of enzyme, which in the Ca2+-bound form plays an important role in the maintenance of the catalytically active enzyme conformation.