Partial purification and characterization of soybean seed arylamidase activity

The arylamidase activity of a soybean seed extract was measured using L-aminoacyl-2-naphthylamides and L-Leu-p-nitroanilide. The enzyme preparation was purified 42-fold with 45% yield, by precipitation with 25-75% ammonium sulfate saturation and by ion exchange and gel filtration chromatography. The highest kcat/Km ratio was that of L-Lys-2-naphthylamide (216 s-1 microM-1) and the lowest was that of L-Leu-p-nitroanilide (40 s-1 microM-1). Enzyme activity was inhibited by -SH and -S-S-group reagents while chelating agents had no effect. L-Lysine, L-leucine, puromycin and bestatin were competitive inhibitors and the Ki values found were: 3.5 mM, 0.9 mM, 0.23 mM and 0.8 microM, respectively.