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

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