Uptake and Processing of in vitro Synthesized Mitochondrial Malate Dehydrogenase by Isolated Watermelon Mitochondria

Mitochondrial MDH (EC 1.1.1.37) is synthesized in watermelon cotyledons as a cytosolic, higher molecular weight precursor (41 kd). We now show that the precursor produced in a reticulocyte lysate in the presence of watermelon mRNA, is posttranslationally sequestered by a crude mitochondrial fraction or by mitochondria purified on Percoll® gradients. It is processed to a proteinase resistant form corresponding to the mature subunit (38 kd). Optimal incorporations are obtained with organelles from early stages of seedling development. An uptake of the mature MDH dimer to a proteolytically protected form could not be detected.