The estimation of phenylalanine ammonia-lyase (PAL)-activity in intact cells of higher plant tissue

Summary A procedure is described which permits the estimation of the relative activity of phenylalanine ammonia-lyase (E.C. 4.3.1.5.) in intact plant cells, exemplified by buckwheat hypocotyls. Hypocotyl segments are incubated at pH 5.5 with L-3-³H]phenylalanine. N³HH₂, which is liberated from phenylalanine by the action of phenylalanine ammonia-lyase, equilibrates with tissue water to yield ³HOH, which is recovered by sublimation. Participation of phenylalanine transaminase in the reactions leading to ³HOH formation is excluded, and it is conclusively shown that ³HOH is formed intracellularly and not by enzymatic activity leaking out of wounded tissue.Abbreviation PAL phenylalanine ammonia-lyase (E.C. 4.3.1.5.)