Relationships between phosphoenolpyruvate synthesis and glutamine formation in isolated chicken liver mitochondria

The rate of phosphoenolpyruvate (PEP) and glutamine (Gln) formation was measured under different conditions in isolated chicken liver mitochondria. Glutamate (Glu) added as a sole substrate in high concentrations (30 mM) to the incubated mitochondria is preferentially metabolized to Gln, but Asp and PEP are also formed. Glu (10 mM) inhibited the rate of PEP formation from malate by about 25%. The effect was potentiated by NH4Cl (10 mM). Neither Glu nor NH4Cl affected the rate of PEP formation from malate by isolated guinea-pig liver mitochondria. Methionine S-sulfoximine, an inhibitor of Gln synthetase, did not reverse the inhibitory effect of Glu of PEP formation from malate in chicken liver mitochondria. The data are discussed in terms of possible interrelationships between uricogenesis and gluconeogenesis in chicken liver.