Apple peels (0.5 g fresh weight) were ground in a mortar and pestle with 10 ml of the cold 0.1 M borate buffer (pH 8.8) containing 2-mercaptoethanol (20 mM) and 0.4 g Polyclar AT per gram fresh weight of apple peels. The extract was centrifuged at 20000× g for 30 min at 4 C. Proteins were precipitated from the supernatant with ammonium sulfate (70% satu-ration) and pelleted by centrifuging for 15 min as described above. The resulting precipitate was gently resuspended in 5 ml of cold borate buffer and used as the enzyme solution. The assay mixture (3 ml) consisted of 0.1 M borate buffer (pH 8.8), 20 µM L-phenylalanine, and enzyme solution containing 50-100 µg protein. All reactions were equilibrated for 10 min at 40 C. The change in A290 over 60 min was used to determine PAL activity. Linearity by the method of Bradford (1976) using bovine serum albumin as a standard. PAL activity was expressed as nkat mg-1 protein.