Changes in intracellular levels of fructose 2,6-bisphosphate and several glycolytic intermediates in Leishmania major promastigotes as a function of pO2

Leishmania major promastigotes were grown to late log phase, washed and resuspended in Hanks' balanced salt solution, and incubated with glucose at various pO2s in the presence of 5% CO2. Samples were taken at times from 0-40 min and assayed for fructose 2,6-bisphosphate (Fru(2,6)P2), glucose-6-phosphate (G6P), fructose-6-phosphate (F6P), phospho(enol)pyruvate (PEP), and ATP. At 95% O2 ATP remained constant throughout the incubation. It did not decrease significantly at 10% O2, but decreased by about 20% and 30% at 6% and 0% O2, respectively. At 95% O2, Fru(2,6)P2 increased about 15-fold within 5 min after the addition of glucose and remained at this high level. At 10%, 6%, and 0% O2 Fru(2,6)P2 rose about 5-fold within 5 min and then declined slightly during the remainder of the incubation. G6P increased from about 0.5 to 12 nmol (mg protein)-1 at 5 min in cells incubated under 95% O2 and then declined to about 5 nmol (mg protein)-1. It increased to about 8 nmol (mg protein)-1 at 5 min and then declined slightly in cells incubated under 10% O2. F6P levels were approximately one-eighth of G6P levels under all conditions, suggesting that phosphohexoseisomerase was not subject to regulation. PEP levels were initially high, but at 95% O2 there was a 50% drop in PEP at 5 min, while at 10%, 6%, and 0% O2 there was less of a decline. The observation that the rise in Fru(2,6)P2 levels at 10%, 6%, or 0% O2 is the same at 5 min and less than the rise at 95% O2 supports the presence of a low affinity oxygen sensor. The different time course of changes in G6P, F6P, and PEP levels suggests that in addition to an activation of pyruvate kinase by Fru(2,6)P2, other regulatory events are also operative at low pO2.