Fig. 4.

Sucrose‐to‐starch carbon partitioning and anaplerotic carbon flux into the Calvin–Benson cycle. Green: enzyme reactions proposedly introducing D isotope signals at glucose H¹ and H². G6PD has a kinetic isotope effect of α _D = k _H/k _D = 2.97 (Hermes et al., ¹⁹⁸²), while PGI has a kinetic isotope effect of 2.22 in the F6P to G6P direction and an equilibrium isotope effect of 1.11 in G6P (Rose & O’Connell, 1961; Wieloch et al., ^2022a). Dashed arrows: intermediate reactions not shown. Enzymes: 6PGD, 6‐phosphogluconate dehydrogenase; G6PD, glucose‐6‐phosphate dehydrogenase; and PGI, phosphoglucose isomerase. Metabolites: 3PGA, 3‐phosphoglycerate; 6PG, 6‐phosphogluconate; 6PGL, 6‐phosphogluconolactone; ATP, adenosine triphosphate; F6P, fructose 6‐phosphate; G6P, glucose 6‐phosphate; NADPH, nicotinamide adenine dinucleotide phosphate; Ru5P, ribulose 5‐phosphate; RuBP, ribulose 1,5‐bisphosphate; and TP, triose phosphates (glyceraldehyde 3‐phosphate, dihydroxyacetone phosphate).