Addendum to a new mathematical approach to metabolism of [14C]glucose: the pyruvate carboxylase reaction

—Previously published equations for analysis of ¹⁴C]glucose metabolism assumed that products of glycolysis enter the citric acid cycle only through acetyl-CoA (Larrabee , 1978). These equations are now extended to include entrance into the citric acid cycle through the pyruvate carboxy-lase reaction as well as via acetyl-CoA and are applied to previously reported data from dorsal root ganglia of 15-day-old chicken embryos. The rate of output of labelled CO₂ in the presence of 2-¹⁴C] glucose could not be accounted for if the flux rate into the citric acid cycle through the pyruvate carboxylase reaction was assumed to be more than about 10–15% of that through acetyl-CoA. It is concluded (1) that the pyruvate carboxylase reaction is a relatively minor source of material for the citric acid cycle in these ganglia and (2) that the previous conclusions about ¹⁴C]glucose metabolism, which ignored the pyruvate carboxylase reaction, need not be modified in the light of this reanalysis.