NADP-specific malate dehydrogenase and glycerate kinase in leaves and evidence for their location in chloroplasts

The operation of both malate dehydrogenase and glycerate kinase in certain phases of photosynthesis has been implied from previous studies. Malate has been recognized as a quantitatively minor photosynthetic product in algae and some plants in which the Calvin cycle is operative (Calvin and Bassham, 1962), and as an intermediate in the C4-dicarboxylic acid pathway of photosynthesis (Hatch and Slack, 1966; Hatch, Slack and Johnson, 1967; Johnson and Hatch, 1968). Although NADP appears to be the predominant pyridine nucleotide in chloroplast oxidation-reduction reactions, an NADP-malate dehydrogenase has been found neither in leaves nor indeed from any other source. A glycerate kinase appears not to have been reported previously from plant tissues although it has been proposed to operate in the glycollate pathway, the photosynthetic bypass cycle in which glycollate derived from sugar phosphates is apparently converted to 3-phosphoglycerate (Tolbert, 1963). Glycerate kinase has been detected in liver and yeast (Black and Wright, 1956; Ichihara and Greenberg, 1957). This communication reports the presence of an NADP-specific malate dehydrogenase and a glycerate kinase in leaves of both Calvin cycle plants and plants in which the C4-dicarboxylic acid pathway is operative. Some properties of these enzymes are described and evidence for their location in the chloroplasts of maize leaves is presented.