Phospholipase D from soybean (Glycine max L.) suspension-cultured cells: purification, structural and enzymatic...

Phospholipase D (phosphatidylcholine phosphatidohydrolase EC 3.1.4.4) from soybean (Glycine max L.) suspension-cultured cell was purified around 1,200-fold to homogeneity by acetone precipitation, Macro-Prep High Q anion exchange, and octyl-Sepharose CL-4B affinity chromatography. The purified enzyme released 1,600 mumol of choline per min per mg of protein. The enzyme is monomeric with a molecular mass of 92 kDa, as estimated by SDS-PAGE. One of the most interesting characteristics of the purified soybean phospholipase D was the dependence of the pH optimum on the Ca2+ ion concentration in the assay. With 10 mM, 20 mM and 40 mM Ca2+ ions, the optima were at pH 7.5, 6 and 5.5, respectively. The specific adsorption of phospholipase D onto octyl-Sepharose gel suggests that the molecule becomes more hydrophobic in the presence of Ca2+ ions. The amino acid sequence of the first 18 N-terminal residues of soybean phospholipase D revealed a high degree of homology with those previously published for cabbage leaf and castor bean endosperm enzymes. Western blots of the soybean phospholipase D showed an immunoreactivity with antibodies raised against a synthetic peptide corresponding to the 15 N-terminal amino acid residues of phospholipase D from cabbage leaves.