Rat brain malic enzyme: subcellular distribution and kinetic studies from two brain regions.

1. The subcellular distribution of malic enzyme in two different brain regions (frontal cortex and striatum) is studied in adult rats. 2. A bimodal distribution is found in both regions: 75% being localized in the mitochondrial fraction and the remaining 25% in the cytosol. 3. In the frontal cortex, free mitochondria is enriched with the enzyme, while, in striatum, free as well as synaptic mitochondria, presented the same activity. 4. Kinetic studies of the malic enzymes show two Km values when malate is used as substrate. A higher Km value for free mitochondria as compared with a lower one found for the cytosolic and synaptosomal mitochondria suggests the presence of two enzyme populations. 5. The following are common characteristics for the two enzyme populations: NADP dependence, use of either Mg2+ or Mn2+ as cofactor and hyperbolic malate saturation curves not affected by dicarboxylic acids.