Purification and properties of phenylalanine ammonia-lyase from leaf mustard

Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5), the first enzyme in phenylpropanoid biosynthesis, catalyzes the elimination of ammonium ion from L-phenylalanine. In the present study, PAL was purified through ammonium sulfate fractionation, DEAE-cellulose chromatography, Sephadex G-200 chromatography, and Q-Sepharose chromatography from the cytosolic fraction of leaf mustard (Brassica juncea var. integrifolia). It consists of 4 subunits, each having an estimated molecular weight of about 40,000 on SDS-polyacrylamide gel electrophoresis (SDS-PAGE). The optimal pH and temperature of the purified enzyme are 9.0 and 45 degrees C, respectively. Its activity is inhibited by Zn2+ ion, and it is strongly activated by caffeic acid. The purified PAL seems to have some characteristics different from those obtained with other PALs.