Grape (Vitis vinifera L.) Malate Dehydrogenase. I. Intracellular Compartmentation of the Isoforms

Intracellular compartmentation of malate dehydrogenase (MDH) isoforms has been studied in grape berries. Cell-organelles and cytosolic compartments have been separately extracted from four different cultivars. Purification of mitochondria has been performed using centrifugations on Percoll gradients with no significant cross-contamination between the obtained extracts. Cytosolic and mitochondrial MDH isoforms were distinguished from their isoelectric focusing profiles in a liquid medium. The acidic (pl between 4.0 and 5.5) and the less acidic isoforms (pl between 5.5 and 7.5) were, respectively, assigned to cytosolic and mitochondrial compartments, taking into account results from analysis with marker enzymes and from literature data. The major MDH isoform in each cytosolic and mitochondrial compartment had a pl near 4.9 and 6.0, respectively, with the same molecular weight (80 000). The presence of these mitochondrial MDH isoforms depended on the cultivar or tissue and the modulation of their expression during the fruit differentiation was considered.