[Photoregulation of L-phenylalanine ammia-lyase: an immunochemical approach]

The photoregulation of L-Phenylalanine ammonia-lyase (PAL) is studied by immunochemical methods. We used a partly purified L-Phenylalanine ammonia-lyase: F1 light fraction, the corresponding inactive one provided from dark-grown cotyledons: F1 dark fraction and the antisera specific of these two fractions. The complete absorption of PAL activity from F1 light fraction with the anti-F1 light immune serum shows the antigenicity of PAL and the specificity of this serum for all forms of PAL present in F1 light fraction. The presence of an inactive L-Phenylalanine ammonia-lyase in the 36 h dark-grown cotyledons suggested by preliminary results of absorption is conformed by showing that less PAL activity is precipitated from the fraction F1 light by a same amount of IgG anti-F1 light when F1 dark fraction is added. This result is explained by a competition between active and inactive forms of PAL for the IgG extracted from an immune serum specific for F1 light fraction. By measuring the absorption of PAL activity from FO fraction (crude extract) obtained from 18 h, 36 h and 48 h light-grown cotyledons when increasing amounts of IgG anti-F1 36 h light are added, we demonstrate the presence of at least two isozymes A and B, the synthesis of B being shifted in time in comparison to A.