Fig. 1.

Schematic highlighting the effects of incomplete triose phosphate isomerase (TPI) exchange and transaldolase (TA) exchange on the distribution of glucose ¹³C isotopomers (●, ¹³C; ○, ¹²C) and ¹³C enrichment of glucose carbon 3 and 4 positions (highlighted by the boxes) from [U-¹³C]glycerol and [1-¹³C]acetate. Glucose isotopomers favored by partial TPI exchange only (A) and TA activity in the presence of complete TPI exchange (B) are indicated by the bold arrows. When TPI exchange is complete, the 2 tracers generate equivalent glucose ¹³C3/¹³C4 ratios, and these are modified in the same manner by TA exchange (i.e., ¹³C3/¹³C4 < 1.0). DHAP, dihydroxyacetone phosphate; G6P, glucose 6-phosphate; FBP, fructose 1,6-bisphosphate; F6P, fructose 6-phosphate; GA3P, glyceraldehyde 3-phosphate.