The role of mitochondrial pyruvate transport in the control of lactate gluconeogenesis.

At low L-lactate concentrations, plots of the reciprocal of the gluconeogenic rate vs hydroxycyanocinnamate concentration were linear up to high inhibitor concentrations, indicating that the pyruvate transporter was a rate-limiting step and alternate pathways were at best minor. At 10 mM L-lactate and in the absence of added acids, the 1/V vs I plots became sigmoidal, indicating both some excess capacity of the transporter, and a significant alternative pathway. Use of transaminase inhibitors suggests that the alternate pathway does not primarily involve a dual glutamate-pyruvate transaminase mechanism.