1. The reoxidation of cytosolic
NADH was studied in a line of human
hepatoma cells (HuH13) whose mitochondria preferentially utilized
glutamine for
ATP formation. 2. The
tumor cells showed mitochondrial reoxidation of
NADH, as evidenced by the accumulation of
pyruvate, when incubated aerobically with L-
lactate. The involvement of the respiratory chain was demonstrated by the addition of specific inhibitors. 3.
Glutamine oxidation proceeded in the
tumor mitochondria exclusively via a pathway involving transamination.
Malate stimulated
aspartate production from
glutamine. 4. When the
tumor cells were cultured in Eagle's medium with
aminooxyacetate or in the absence of
glutamine, a marked reduction in the cellular
NAD/
NADH ratio was observed. 5. These results indicate that the
malate-
aspartate shuttle was functioning in the
tumor cells.