An acid phosphatase gene (aphA gene) from an industrial miso koji mold strain, A. oryzae KBN630, was disrupted by using the recently developed homologous gene replacement system for this strain. The aphA gene disruption did not affect growth on steamed soybean. Acid phosphatase production decreased by approximately 20% in the aphA gene disruptants compared with that of the wild-type strain. Utilizing the promoter of the A. oryzae TEF1 gene, AphA expressed in A. oryzae was successfully secreted into the culture medium. AphA had a molecular mass of 58.0 to 65.0 kDa, a pH optimum of 4.0, and a temperature optimum of 40℃. AphA had the ability to release inorganic phosphate from GMP and IMP. This is the first report to show directly that an A. oryzae acid phosphatase has the ability to hydrolyze GMP and IMP.

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