Malic enzyme isoforms in astrocytes: comparative study on activities in rat brain tissue and astroglia-rich primary cultures.

Anion exchange chromatography on diethylaminoethyl cellulose was optimized to separate the cytosolic and mitochondrial isoforms of malic enzyme from rat brain. Extracts of adult rat brain and of astroglia-rich primary cultures derived from the brains of newborn rats were analyzed for their content of the two isozymes. In the case of brain tissue 45% of malic enzyme activity was due to the cytosolic isoform. In contrast, in extracts from astroglia-rich primary cultures more than 95% of the total activity was associated with the cytosolic isozyme. From these data it is concluded that the cytosolic rather than the mitochondrial isoform of malic enzyme has prominent functions in astroglial metabolism.