A 2ND FORM OF PHENYLALANINE AMMONIA-LYASE FROM LEAF MUSTARD

Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) catalyzes the eliminatio n of ammonium ion from L-phenylalanine in a variety of plants and fung al species. PAL was previously purified and characterized from leaf mu stard in our laboratory. In the present study, me purified a second ph enylalanine ammonialyase (PAL II) from leaf mustard by a combination o f ion exchange chromatography and gel filtration, PAL I and PAL II mig rate at a different rate on native polyacrylamide gel electrophoresis, It consists of four subunits, each having the molecular mass of about 37,000 Da, Its isoelectric point and K-m value for L-phenylalanine we re found to be 5.4 and 3.8 x 10(-5) M, respectively, The purified enzy me has an optimum pH and temperature of 8 and 45 degrees C, respective ly. It is activated about 2-fold by caffeic acid (1 mM), whereas it is inhibited to 15% by Zn2+ (1 mM). However, the physiological role of P AL II remains unknown.