Essential for sperm motility and male fertility but is not required for the completion of spermatogenesis. (2R)-3-phosphoglycerate + ATP = (2R)-3-phospho-glyceroyl phosphate + ADP Carbohydrate degradation; glycolysis; pyruvate from D-glyceraldehyde 3-phosphate: step 2/5. Monomer. Testis specific. Expression is highest in the adult, lower in a 10 month old and very weak in an 8 week old. Contains at least 10 polymorphisms. Those that lead to amino acid substitutions may alter protein secondary structures and may influence male fertility. Belongs to the phosphoglycerate kinase family.