Die zeitliche Dauer der Isocitrat-Lyase-Synthese in Kotyledonen von Wassermelonenkeimlingen

Summary Previously, it was deduced from inhibitor experiments that isocitrate lyase (EC 4.1.3.1.) is synthesized de novo in watermelon cotyledons during the first 3 days of germination, which explains the sharp increase of activity during this period. The following decrease of activity was interpreted as the result of a limited half life of the enzyme molecule (Hock and Beevers, 1966).This hypothesis has been confirmed now by density labeling experiments of isocitrate lyase with deuterium. Seedlings grown from day 0 on D₂O (80 vol. %) contained a heavier enzyme at the time of maximum activity than control seedlings grown on H₂O (Fig. 6). No incorporation of deuterium into isocitrate lyase, however, was detectable when the cotyledons were labeled only from day 3 1/2 on, i.e. after the stage of maximum activity had been passed (Fig. 10), in spite of the fact that D₂O was taken up from the cotyledons in considerable quantities. —These results prove at the same time that density labeling of the isocitrate lyase during early stages of germination was a result of de novo synthesis rather than a mere artifact produced by isotopic exchange.An improved method for the purification of isocitrate lyase from higher plants is introduced.