CHARACTERIZATION OF A MITOCHONDRIAL NADP-DEPENDENT ISOCITRATE DEHYDROGENASE IN AXES OF GERMINATING SUNFLOWER SEEDS

An NADP-dependent isocitrate dehydrogenase (NADP-IDH) activity was mea sured in a Percoll purified mitochondrial fraction from axes of germin ating sunflower (Helianthus annuus, L.) seeds. Fraction enrichment in mitochondria was revealed by marker enzyme activities and by electron microscopy which showed no contamination by other organelles and indic ated that no fragmentation of mitochondria had occurred during their p reparation. More than 95% of the NADP-IDH activity was latent; it was found to be different from the mitochondrial NAD-IDH activity by com p etition assay. Mitochondrial NADP-IDH was electrophoretically and immu nologically different from the NAD-specific and the cytosolic NADP-spe cific isoforms. The enzyme activity from mitochondrial matrix extract was eluted from Superose 12 with a molecular weight of 70 kDa. A possi ble physiological role of the mitochondrial NADP-IDH is discussed.