Presence and partial characterization of internal acid protease of Aspergillus oryzae

The presence and partial characterization of the internal acid protease (EC 2.4.23.6) of Aspergillus oryzae has been investigated. Although the majority of the acid protease is external and present in the culture filtrate, a significant amount of the active enzyme is firmly bound to the cells; it is not released by repeated extraction of cells with 0.9% sodium chloride but is liberated into the soluble fraction during disruption of cells. The internal acid protease, as well as the external one, was separated into two major molecular forms (F1 and F2) with molecular weights of 60,000 and 42,000, respectively, by chromatography on Sephadex G-100 and on CM-Sephadex C-50. The partially purified internal enzymes had the same catalytic and immunological properties, as did the external enzyme.