Serine is a natural ligand and allosteric activator of pyruvate kinase M2

The M2 isoform of pyruvate kinase (PKM2) is a key glycolytic enzyme that is overexpressed in cancer cells; here, serine is shown to bind to and directly activate PKM2, and the resulting reduction in enzyme activity under serine-deprivation conditions is shown to lead to the diversion of glucose-derived carbon to promote serine biosynthesis required for cell proliferation.