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Relative Activities of NAD- and NADP-Isocitric Dehydrogenases in Bean Mitochondria Modified by Glycerol or NADP ¹

^a Biological Institute, Faculty of Science, Nagoya University, Nagoya, Japan

Mitochondria from cotyledons of Vigna sesquipedalis (L.) Fruwirth (starchy seed) showed no NAD-isocitric dehydrogenase (NAD-IDH) activity by the methods which have been known to be useful for the detection of NAD-IDH in mitochondria of plants including castor bean and alaska pea. When the Vigna cotyledon mitochondria were treated with glycerol, NAD-IDH activity appeared and NADP-isocitric dehydrogenase (NADP-IDH) activity was inhibited. The inhibition of mitochondrial NADP-IDH by glycerol was overcome by the addition of excess NADP.

On the other hand, NADP-IDH activity in the soluble fraction of cell components was only slightly inhibited by glycerol and no NAD-IDH activity was elicited.

It was postulated that NADP-IDH in mitochondria is converted to NAD-IDH by glycerol and back to NADP-IDH with NADP by the alteration in the spatial configuration of the enzyme. However, there could be 2 proteins as the other possibility.

The NADP-IDH in the soluble fraction which is not subject to such alteration is different from the mitochondrial NADP-IDH.