Activity of Isocitric Dehydrogenase in the Fat Bodies of the Cockroach, Leucophaea maderae (F)

Abstract

ISOCITRIC dehydrogenase, an enzyme of the tricarboxylic acid cycle, is responsible for the formation of α-ketoglutarate from isocitrate. During the reaction, oxalosuccinate is formed (as an intermediate) owing to the presence of two pyridine nucleotide-linked dehydrogenases in biological systems. One dehydrogenase is linked with NAD and the other is linked with NADP. They first catalyse the oxidation of isocitrate, and then its decarboxylation in the presence of the manganous ion. If NADP is used in the reaction, it is reduced and, because of the reversibility of the process, carbondioxide is fixed in oxalosuccinate and isocitrate. Isocitric dehydrogenase has been isolated from heart tissue of the pig¹, yeasts², and various animal tissues³. This enzyme was discovered in the supernatant fraction of the homogenates of the fat bodies of the cockroach, Periplaneta americana^4,5. Its presence has been reported in the haemolymph of the mealworm, Tenebrio molitor, by Prota (see previous communication). Hence, the purpose of this investigation was twofold: to determine whether this enzyme could be detected in normal and aposymbiotic fat bodies of the cockroach, Leucophaea maderae; and to determine whether the presence of the enzyme in this tissue is due to the action of the tissue, the symbionts or both.