Pyruvate kinase (PK) is a key enzyme in glycolysis, existing in four isoforms: L (liver), R (red blood cells), M1 (muscle), and M2 (embryonic and tumor cells). Located in the cytoplasm, it catalyzes the conversion of pyruvate, playing a crucial role in glucose metabolism. The M2 isoform promotes proliferation by facilitating lactate fermentation in tumor cells. PK gene expression is regulated by tissue-specific mechanisms, and its aberrant expression is associated with diseases such as tumor metabolism and hereditary hemolytic anemia. Mutations affecting its activity disrupt energy metabolism, influencing cell growth.