Four Pyruvate kinase(PK) iso forms exist in mammals: the L and R iso forms (from the PKLR gene) are expressed in liver and red blood cells respectively, and the PKM gene encodes two splice variants, the Ml isoform that is expressed in most adult tissues, and the M2 isoform that is expressed during embryonic development and in some adult tissues including the kidney and hematopoietic stem cells. Many tumor cells also express PKM2. This tetrameric allosterically regulated isoform is intrinsically designed to downregulate its activity, through post-translational modification, allosteric modulation by small molecule ligands including some amino acids, and by subunit dissociation (into the dimeric form), which results in partial inhibition of glycolysis at the last step[1].