Acid Phosphatases from Fusarium moniliforme

II. Further Studies on Substrate Specificity and Mode of Action of Acid Phosphatase II

Abstract

1. The substrate specificity of acid phosphatase II [different from EC 3. 1. 3. 2 enzyme] from Fusarium moniliforme was studied. Good substrates of the enzyme so far examined could be divided into four classes; i.e. aryl phosphates, nucleotides, phosphoenolpyruvate, and terminal pyrophosphates. Both phosphomonoesters and diesters of aryl phosphates and nucleotides were hydrolyzed.
2. The kinetic parameters, K_m and V_max, of acid phosphatase II for p-nitrophenyl phosphate, phenyl phosphate, phosphoenolpyruvate, and inorganic pyrophosphate were determined at pH5.3. For adenosine 3'-phosphate, the upper and lower limits of the K_m and V_max values, respectively, were estimated at the same pH. The ratio, V_max/K_m, for adenosine 3'-phosphate was highest, and those for phosphoenolpyruvate and inorganic pyrophosphate were considerably lower.
3. β-Glycerophosphate, glucose 1-phosphate, and glucose 6-phosphate were competitive inhibitors of the hydrolysis of p-nitrophenyl phosphate by acid phosphatase II.
4. Adenosine, guanosine, and cytidine and, to lesser extents, uridine, adenine, and p-nitrophenol inhibited the hydrolysis of p-nitrophenyl phosphate by acid phosphatase II. Inhibition by adenosine was non-competitive.
5. Acid phosphatase II can be regarded as a new enzyme because of its unique substrate specificity. The mode of action of the enzyme was discussed.