De Novo Synthesis of Isocitritase in Peanut (Arachis hypogaea L.) Cotyledons

Germination of peanut seed is accompanied by a rapid increase in isocitritase (isocitrate lyase, EC 4.1.3.1) during the first 4 days. The presence of cycloheximide (50 μg/ml) during water imbibition inhibited the increase in isocitritase activity. Actinomycin D conversely did not inhibit isocitritase activity until the second day of imbibition while RNA synthesis was inhibited. Germination of peanut seed in ¹⁴C-reconstituted amino acids followed by fractionation of a 20 to 35% ammonium sulfate preparation on a Sephadex G-200 column (57-fold purification) showed that the active enzymic fraction coincided with a large peak of radioactivity. Germination of peanut seed in 45% D₂O followed by enzyme purification and CsCl equilibrium centrifugation revealed that all the enzyme from D₂O seed had a higher density than normal isocitritase. These data indicate that isocitritase in peanut seed is synthesized de novo.