Figure 1.

Simplified metabolic scheme showing the potential fates of pyruvate and the labeling pattern after ¹³C-3-pyruvate addition to illuminated leaves. The labeled position in C-3-pyruvate and molecules downstream through PDH (1), AlaAT (2), and the tricaboxylic acid cycle is shown in black. Labeled C-atom positions coming from PPDK (4) or reverse pyruvate kinase (PK, 3) activity are shown in gray. The small gray-labeled C atom accounts for the fumarate/malate equilibrium that interconverts C-2 and C-3 atoms due to molecular symmetry. This scheme does not take into account multiple turns of the tricarboxylic acid cycle and assumes little conversion of 2-oxoglutarate to fumarate (dashed arrow, see main text and Tcherkez et al., 2009). AspAT, Asp aminotransferase; Fase, fumarase; MDH, malate dehydrogenase.