The estimation of phenylalanine ammonia-lyase (PAL) activity in intact cells of higher plant tissue : III. Specificity of (3)H-release from L-[2,3-(3)H]phenylalanine and precautions in application of the assay to various tissues.

A previously described procedure for the estimation of relative activities of phenylalanine ammonia-lyase (EC 4.3.1.5) in intact plant cells (Amrhein et al. (1976) Planta 131, 33-40) was reexamined for its specificity and its applicability to various tissues. In buckwheat hypocotyl segments (3)H is stereospecifically released from the pro-3S-position of L-[2,3-(3)H]phenylalanine and is thus due to phenylalanine ammonia-lyase activity. In buck wheat and sunflower leaf disks, however, (3)H release occurs from both the 2- and 3-positions of the labeled substrate and can only partially be attributed to phenylalanine ammonia-lyase activity.