The acid phosphatase(EC 3.1.3.2) of $\mbox{\underline{Aspergillus}}$ $\mbox{\underline{niger}}$ was an orthophosphate-repressible enzyme; in a high phosphate medium, little acid phosphatase was produced, and in a low phosphate medium, the production of acid phosphatase was increased. Medium containing 10mg of phosphate per 100ml was optimal, and the amount of acid phosphatase produced in this medium was about 20 times of one produced in the medium containing 60mg of phosphate per 10ml.
Acid phosphatase was extracted from mycelium of $\mbox{\underline{Aspergillus}}$ $\mbox{\underline{niger}}$ which was grown in the 10mg phosphate per 100ml medium. This enzyme was separated into two fractions(acid phosphatase I and II) by DEAE-cellulose ion-exchange chromatography and further purified by Sephadex G-150 gel filtration. They were purified about 40- and 15-fold, respectively.
The partially purified enzymes hydrolyzed 1300, and 463 umoles of p-nitrophenylophosphate (NPP) per minute per mg protein and Km values for NPP were $5.3×10^{-4}$M and $2.5×10^{-4}$M, respectively.
The activity of acid phosphatase I and II were optimal at pH 5.0 and 2.0. They did not require the presence of divalent cations. Inorganic orthophosphate and potassium fluoride competitively inhibited hydrolysis of NPP.
Acid phosphatase I hydrolyzed NPP, phosphoenolpyruvate, 5'-AMP, glucose 6-phosphate and acid phosphatase II hydrolyzed NPP, phosphoenolpyruvate, glucose 6-phosphate, pyridoxal 5'-phosphate at maximal rates, while having very little activity for ATP, ADP, and adenosine cyclicphosphate.
The molecular weight of partially purified acid phosphatase I and II were estimated to be 200,000 and 300,000 respectively.
