ocalization, properties and time courses of malate dehydrogenases in greening radish cotyledons were studied as well as an inhibitory effect of 4-thiouridine upon the enzymes. Results obtained are as follow.
1) Chloroplast fraction isolated from the radish cotyledon cells contained <NAD>^+ specific malate dehydrogenase, the specific activity of which decreased as the development of the chloroplast proceeded on illumination.
2) Non-chloroplast fraction contained <NADP>^+-malate dehydrogenase and malic enzyme. Cofactor of the <NADP>^+_malate dehydrogenase could be replaced by <NAD>^+ with a slight decrease of the specific activity. Malic enzyme required <NADP>^+ as a specific cofactor. Specific activities of both the enzymes remained unchanged with illumination time.
3) <NAD>^+_malate dehydrogenase of the chloroplast was inhibited by the presence of 4-thiouridine (1-5mM), but malic enzyme in the cytoplasm was not.
Based upon these observations, biological significance of <NAD>^+_malate dehydrogenase in the developing chloroplast was discussed.