Evidence for the presence of membrane-bound forms of acid protease in Aspergillus oryzae.

While approximately 85% of the cell-bound acid protease of $\text{Aspergillus oryzae}$ were recovered in the soluble fraction upon disruption of cells, the rest of the enzyme was found to be present tightly associated with the membranes. Two forms of membrane-bound enzyme, which were solubilized with Triton X-100, were similar to the external acid protease found in culture medium in that they had an optimum pH at 3.2, activated trypsinogen at pH 3 and lost their activity upon treatment with 5.1 mM sodium dodecylsulfonate. However, they differed in their hydrophobic properties (i.e. aggregation in the absence of Triton X-100 and activation by the detergent) from both the cell-bound, soluble form and the one excreted into culture medium.