[Organ specific multiple forms of glutamic dehydrogenase in Medicago sativa]

The alteration of the multiple forms of NAD-dependent glutamic dehydrogenase (GDH) during the development of Medicago sativa is investigated by means of polyacrylamide electrophoresis. Seed germination is accompanied by a characteristic change of the GDH-isoenzyme pattern. Seeds contain seven isoenzymes, which gradually decrease in number during germination. At the same time a pattern of new isoenzymes becomes visible. The seed pattern is called GDH-I and the later appearing pattern GDH-II. GDH-I is characteristic for the cotyledons, whereas GDH-II is the typical pattern of the root system. Shoots produce a mixed pattern composed of the GDH-II isoenzymes as well as some GDH-I isoenzymes.These isoenzyme patterns are organ specific. No qualitative change occurs during further development of the plants and during growth in the presence of different inorganic and organic N-sources in the culture medium.All the individual isoenzymes are found predominantly in the particulate fraction. They represent stable forms which are not altered by variation of the conditions of enzyme extraction or during enzyme purification. Re-electrophoresis of the individual isoenzymes following elution from the polyacrylamide gels reveals only one specific band. The molecular weights of all the distinctive isoenzymes are identical.There is some evidence that the different isoenzymes represent conformational forms of one enzyme, and it is postulated that the GDH-I isoenzymes are correlated to a normal metabolic (or catabolic) function of the enzyme, whereas the GDH-II isoenzymes are responsible for a primarily anabolic function of glutamic dehydrogenase.