The metabolism of l[3-3H]lactate by isolated hamster liver cells

The rate of tritium removal from l3-³H]lactate by hamster liver cells is faster than the analytical rate of lactate utilization, or the rate of ¹⁴C disappearance from lU-¹⁴C]lactate, with the result that the ³H/¹⁴C ratio in residual lactate from l-U-¹⁴C,3-³H]lactate decreases. However, addition of low concentrations (0.1 to 1.0 mM) of l-cycloserine, a glutamate pyruvate transaminase inhibitor, nearly equalizes the rates of isotope utilization from l-3-³H]lactate and l-U-¹⁴C]lactate. The results suggest a very limited rate of recycling of phosphoenolpyruvate back to pyruvate during gluconeogenesis from lactate in fasted hamster liver cells.