Inhibition of acid phosphatase isoforms purified from mature soybean (Glycine max) seeds.

The four soybean seed acid phosphatase isoforms AP1, AP2, AP3A and AP3B were competitively inhibited by phosphate, vanadate, fluoride and molybdate, using p-nitrophenylphosphate as substrate. The four isoforms were not significantly affected by compounds that can interact with SH residues or by pyridoxal phosphate. These results indicated that cysteine and lysine residues are not present in the active site of the four soybean seed acid phosphatase isoforms. The inhibition constant values for phosphate, vanadate, fluoride and molybdate at pH 5.0 were respectively: API (250, 12.8, 1.7, 0.05 microM). AP2 (800, 10, 500, 0.025 microM), AP3A (250, 24.2,250, 0.032 microM ), AP3B (2400 36.9, 750, 0.05 microM).