Rice Bean (Vigna umbellata Thunb.) Acid Phosphatase: Effect of Metal Ions and Metabolites

Abstract

Rice bean acid phosphatase dialyzed against ethylenediaminetetracetic acid (1 mM), yielded no loss in activity at 0.5 mM p-nitrophenylphosphate. It had a mild activating effect at 0.1 mM p-nitrophenylphosphate. Divalent cations belonging to group II of Periodic Table like Mg2+, Ca2+, Sr2+, and Ba2+ at 0.5 mM concentration p-nitrophenylphosphate did not affect the enzyme activity. At 0.1 mM p-nitrophenylphosphate, however, only Mg2+ ions showed little inhibition. The transition metal ions viz. Zn2+ , Cu2+, Co2+, Mn2+ and Fe3+ showed inhibition at both pnitrophenylphosphate concentrations. Na+ , K+ , and NH4 + ions did not influence the enzyme activity, but Li+ inhibited the activity at 0.1 and 0.5 mM p-nitrophenylphosphate concentrations, respectively. Molybdate and phosphate anions proved to be strong inhibitors, but vanadate, a moderate inhibitor. Tartrate anion did not exhibit an effect on rice bean acid phosphatase. Sugars, plant hormones, medicines, vitamins, and amino acids at 1.0 mM concentration did not affect the enzyme activity. NADH exhibited the maximum activation, followed by citric acid, isocitrate, and oxaloacetate. Caffeine showed activation in the enzyme activity. Phosphate esters (1-Naphthylphosphate, phenylphosphate, PEP, and ADP) exhibited competitive inhibition when pnitrophenylphosphate was used as a substrate. Non-ionic detergents Triton X-100 and Tween-20 brought activation to the enzyme. The ionic detergent SDS brought complete loss to the enzyme activity. Dithiothreitol brought inhibition to the enzyme activity. The presence of β-mercaptoethanol did not influence the enzyme activity.