Essential for sperm motility and male fertility but is not required for the completion of spermatogenesis (PubMed:19759366). (2R)-3-phosphoglycerate + ATP = (2R)-3-phospho-glyceroyl phosphate + ADP Carbohydrate degradation; glycolysis; pyruvate from D-glyceraldehyde 3-phosphate: step 2/5. Monomer. Testis and sperm. Localized on the principle piece in the sperm (at protein level). Testis-specific. Mice display greatly reduced ATP levels in sperm, severely impaired sperm motility and are infertile. No alteration in testis histology, sperm counts, or sperm ultrastructure seen. Belongs to the phosphoglycerate kinase family.