Gluconeogenesis in the kidney cortex. Quantitative estimation of carbon flow.

Using analytical data and the results of degradation of glucose, lactate, and glutamate produced from [Z-14C]pyruvate or lactate, we have estimated the pathways of carbon flow during active gluconeogenesis in the kidney cortex. This approach involves a steady state model and solution with the aid of a digital computer. By the isotopic method one can estimate the rates of pyruvate carboxylase, pyruvate dehydrogenase, pyruvate kinase, and fumarase exchange and these are compared with rates of gluconeogenesis and the tricarboxylic acid cycle. The cycle involving variations on the scheme [pyruvate 4 oxalacetate + phosphoenolpyruvate + pyruvate] was measured and found to be similar to the rate of glucose synthesis, indicating that net flux through pyruvate carboxylase and phosphoenolpyruvate carboxykinase may be nearly twice the net rate of glucose formation. The rate of fumarase exchange was about four times the net rate of the tricarboxylic acid cycle.