– Phosphoglycerate kinase 1(PGK1) is an enzyme. It is mainly expressed in spermatogonia and Localized on the principle piece in the sperm. Its expression significantly decreased in the testis of elderly men. PGK1 involved in a critical energy-producing process known as glycolysis. It helps carry out a chemical reaction that converts a molecule called 1,3-diphosphoglycerate, which is produced during the breakdown of glucose, to another molecule called 3-phosphoglycerate during glycolysis. PGK1 may also act as a cofactor for polymerase alpha. The protein has been identified as a moonlighting protein based on its ability to perform mechanistically distinct functions.