The reliance on anaerobic glycolytic metabolism as a source of energy and enhanced lactate production relative to untransformed cells are well understood traits of cancer cells. This phenomenon, known as the Warburg effect, is consistent with the results of early proteomic studies, which showed that cancer cells alter the expres- sion of enzymes involved in several metabolic processes, including those that regulate bioenergetic metabolism (Gharbi et al., 2002, Unwin et al., 2003; Zhang et al., 2005; Bi et al., 2006).

Changes in the expression of glycolytic enzymes probably contribute to the ob- served increase of glycolytic flux of cancer cells. In addition to changes in gene expression, posttranslational modifications on metabolic enzymes contribute to the Warburg ef- fect. For example, tyrosine phosphorylation regulates the pyruvate kinase (PK) isozyme PNK2, which is predominantly expressed in fetal tissue and cancer cells (Christofk et al., 2008; Hitosugi et al., 2009). PK catalyses the production of pyruvate and ATP from phosphoenolpyruvate and ADP, a rate limiting step in glycolysis.