 When M2-PK is mainly in the highly active tetrameric form, which is the case in most normal cells, glucose is mostly converted to lactate, with the attendant production of energy.In contrast, the dimeric form of M2-PK has a low affinity for phosphoenolpyruvate, being nearly inactive at physiological PEP concentrations.When M2-PK is mainly in the dimeric form, which is the case in tumor cells, all phosphometabolites above pyruvate kinase accumulate and are channelled into synthetic processes which branch off from glycolytic intermediates, such as nucleic acids, phospholipids and amino acids, important cell building blocks for highly proliferating cells such as tumor cells.