Figure 3.

Positional ¹³C-NMR signals in Glu, after ¹³C-3-pyruvate and/or ¹³CO₂ labeling of illuminated cocklebur leaves for 3 h, under 400 μmol mol⁻¹ CO₂, 21% O₂, 23.5°C, and 300 μmol m⁻² s⁻¹ PAR. A, C-atom numbering in Glu. B, Positional ¹³C abundance (in % ¹³C) in Glu (redrawn from Fig. 2). The natural ¹³C abundance (1.1%) is indicated with the horizontal dashed line. The major origin of ¹³C labeling in each position is indicated with arrows, as discussed in the main text. C, {¹³C-¹³C} spin-spin interactions in Glu. For a given labeled position, numbers between arrows indicate the percentage of C atoms having ¹³C labeling in the neighbor C atoms. Bidirectional arrows indicate that two {¹³C-¹³C} interactions were obtained, demonstrating there were two interacting, labeled neighbor C. For example, in C-3 Glu after pyruvate labeling, the percentage of ¹³C in C-3 that was accompanied by ¹³C in C-2 and C-4 was 62%. In 2-oxoglutarate, {¹³C-¹³C} spin-spin interactions were only visible (distinguishable from the background) in C-4 because of the larger ¹³C enrichment in that position. The value of 1% (Glu C-2 upon ¹³C-pyruvate labeling) is arbitrary and corresponds to the natural interaction (¹³C natural abundance of 1.1%). Bidirectional half arrows indicate that a single {¹³C-¹³C} interaction occurred, on one side only of the C-atom position considered. From top to bottom, interactions values indicated here are that observed after ¹³C-pyruvate labeling, ¹³CO₂ labeling, and after double labeling, in that order.