AbstractUnder certain conditions in polyacrylamide gradient gel electrophoresis (PAGGE), a linear correlation between the logarithm of the size of calibration proteins (log MW or log Rs) and the square root of their migration distance (√D) can be observed; slope and intercept of the calibration curve depend on the duration of electrophoresis; linearity, however, is maintained over a wide range (4‐60 h, 200 V) (Rothe and Purkhanbaba, Electrophoresis 1982, 3, 33–42.) Using this method the reaction of plant isozyme systems penetrating a linear polyacrylamide (PAA) gradient gel was investigated: lactate dehydrogenase (LDH) from potato tubers behaves similarly to animal calibration proteins. The enzyme exhibits 3 subbands with molecular weights of 144 000, 150 000 and 156 000 (± 1.7 %), respectively. The enzyme system “shikimate oxidoreductase” (SORase) behaves significantly different: during PAGGE it splits into 2 major bands (∼60 000 and ∼110 000, respectively) consisting of several subbands. The results of our experiments show that SORase is present in vivo as a complex system. We believe that this complex is partly indentical with the so‐called pre‐