Pyruvate utilization of rabbit reticulocytes--a compartmental study.

The utilization of [2-14C] pyruvate via the citric acid cycle of rabbit reticulocytes was studied to elucidate the importance of carboxylation- and decarboxylation reactions in this cell type. Unknown flux rates were determined by fitting the observed time-dependent labeling of CO2, alanine, glutamate and aspartate (all carbon atoms and C alpha) to the corresponding set of differential equations. The results reveal a high activity of the shuttle rate between mitochondrial pyruvate and the C4 pool catalysed by the pyruvate carboxylase (v = 19.1 nM/ml cells/min) and the malic enzyme (v = 57.5 mM/ml cells/min) which is comparable with the flux rate within the citrate cycle (v2 = 46.2 nM/ml cells/min). Moreover, our studies provide strong indications for the existence of a pyruvate utilizing metabolic pathway which has not been described so far.