Presence of binding site for alpha-amylase and of masking protein for this site on mycelial cell wall of Aspergillus oryzae.

Mycelial cell wall of Aspergillus oryzae M-13 grown in an alpha-amylase-forming medium could not bind alpha-amylase (Taka-amylase A, EC 3.2.1.1). However, by treatment with 1.0 n NaOH at 100 C for 30 min, the wall gained the ability to bind alpha-amylase. This phenomenon was caused by removal of a factor (designated as masking factor) which masked the binding site for alpha-amylase. The masking factor was purified as a preparation giving a single peak in both ultracentrifugation (1.6S) and by gel electrophoresis (M(BPB), 1.0). Approximately 20 mug of the purified factor, bound to 10 mg of the alkali-treated mycelial cell wall, prevented the binding of approximately 100 mug of alpha-amylase or released approximately 100 mug of alpha-amylase which previously was bound to the alkali-treated wall. These findings indicate that the factor has much higher affinity than alpha-amylase for the binding site on the mycelial wall. The masking factor was inducibly formed accompanying the secretion of alpha-amylase.