The activity of the
malate-
aspartate shuttle for the reoxidation of reduced cytosolic
nicotinamide adenine dinucleotide (
NADH) by mitochondria was studied in a line of human
myeloid leukemia cells (K-562). The
tumor cells showed mitochondrial reoxidation of cytosolic
NADH, as evidenced by the accumulation of
pyruvate, when incubated aerobically with L-
lactate. The involvement of the respiratory chain in the reoxidation of cytosolic
NADH was demonstrated by the action of
rotenone,
antimycin A, and
oligomycin which strongly inhibited the formation of
pyruvate from added L-
lactate. Moreover,
pyruvate production was greatly inhibited by the
transaminase inhibitor,
aminooxyacetate. Under glycolytic conditions, in the presence of
aminooxyacetate, the rate of
pyruvate production was also markedly inhibited, the rate of
lactate accumulation was stimulated, and at 60 min the cytosolic
NADH/
nicotinamide adenine dinucleotide (
NAD) ratio had increased progressively about 5-fold with respect to untreated cells. The maximal rate of the
malate-
aspartate shuttle has also been established by addition of
arsenite to inhibit mitochondrial oxidation of the
pyruvate formed from added L-
lactate.