Catalyzes the conversion of D-glyceraldehyde 3-phosphate (G3P) into 3-phospho-D-glyceroyl phosphate in glycolysis and the reverse reaction in gluconeogenesis (By similarity). May play an important role in regulating the switch between different pathways for energy production during spermiogenesis and in the spermatozoon. Required for sperm motility and male fertility (By similarity). . This is the function of Ensembl gene identifier ENSG00000105679 (GAPDHS, glyceraldehyde-3-phosphate dehydrogenase, spermatogenic).