Figure 2.
The metabolic pathways that generate various lactate isotopomers and isotopologues in 4T1 cells, traced by [U-13C] glucose. Besides [U-13C]lactate, there are trace amount of other lactate isotopologues, which could be generated from [U-13C]pyruvate through tricarboxylic cycle to produce [1,2-13C2]malate and [3,4-13C2]malate, which, via catalysis of malic enzyme, generate [1,2-13C2]pyruvate and [3-13C]pyruvate, which can convert to corresponding lactate. [1,2-13C2]pyruvate and [3-13C]pyruvate can enter Krebs cycle, leading to generation of other lactate isotopomers.