Studies on malate dehydrogenases and aspartate aminotransferases from Neurospora crassa

Both mitochondrial and cytoplasmic forms of malic dehydrogenase and aspartate aminotransferase have been demonstrated in extracts of Neurospora crassa. The mitochondrial and cytoplasmic malic dehydrogenases can readily be distinguished from each other, and from the two forms of aminotransferase, by starch gel electrophoresis. Coenzyme analogs were used to demonstrate differences in the catalytic properties of the two forms of malic dehydrogenases. Resolution of Neurospora aspartate aminotransferase and malic dehydrogenase activities was obtained by gel filtration, and the two types of activity showed differing behavior during ammonium sulfate fractionation. The present data strongly implies that in N. crassa aspartate aminotransferase and malic dehydrogenase activities reside in distinct proteins. This is in marked contrast to previous reports that both types of enzymic activity in Neurospora extracts are associated with a single mitochondrial protein.