PC and cancer: Murine 4T1 cancer cells with a propensity for lung metastasis, as well as MDA-MB-231 cells, display significant pyruvate carboxylase expression and activity [33, 34] and hence this reaction could account for 2.1 nmol oxaloacetate/min required to re-oxidize the remaining NADH (see Supplemental Fig. 6 for proposed flux scheme for MDH1 as J6b).