[Changes of activity of isocitritase (E C 4. 1. 3. 1.) during photomorphogenesis in mustard seedlings (Sinapis alba...

In a previous paper (HOCK, KüHNERT and MOHR, 1965) we have shown that fat degradation in the cotyledons of the mustard seedling (Sinapis alba L). is under the control of active phytochrome (=P730), at least to a certain extent. One could imagine that P730 might exert this control over fat consumption through isocitritase (E C 4. 1. 3. 1). In the present paper we demonstrate that P730 does not have any influence on the activity of isocitritase in the mustard seedling, although the enzyme activity does show a strong increase and a following decline during the time of our experimentation (Fig. 8, 9). - Isocitritase could be assayed in a satisfactory manner in the raw extract only after the adsorption of phenolic compounds on "Divergan" (Fig. 1, 3). Furthermore the biological unit of the "seedling" turned out to be the only reliable system of reference for the enzyme activity determined in the extract. Puromycin strongly inhibits isocitritase synthesis whereas Actinomycin D is hardly effective (Fig. 10). It has been concluded that there might exist a relatively stable m-RNA which has been formed during the early stage of germination. Regulation of enzyme synthesis might occur on the level of translation. The evidence for this conclusion is not convincing, however; other interpretations are not excluded.