[Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) of the mustard seedling (Sinapis alba L.), an electrophoretically homogeneous enzyme].

Improved techniques in localization of phenylalanine ammonia-lyase (PAL) on polyacrylamide disk electrophoresis columns indicate that the enzyme synthesized under the control of phytochrome is electrophoretically indistinguishable from the enzyme present in dark grown mustard seedlings. Furthermore, no heterogeneity of PAL with respect to molecular size has been detected. However, the formation of high molecular weight aggregates with PAL activity in tris buffer of low concentration has been demonstrated. The data lead to the conclusion that phytochrome does not induce the synthesis of a novel PAL enzyme differing in its structural properties from the PAL in dark grown seedlings. The observations of other investigators on separable forms of PAL are critically discussed.