Metabolism of Round Spermatids: Pyruvate cannot Maintain the ATP Level: (ATP synthesis/α-ketoacid/rat spermatids)

Round spermatids (steps 1-8) were isolated from rat testes and the effect of pyruvate on their intracellular ATP level was examined. Results showed that although the spermatids consumed a considerable amounts of pyruvate, this substrate alone did not maintain their ATP level. However, their ATP level was maintained in the presence of both pyruvate and α-ketovalerate or α-ketobutyrate. Maintenance of the ATP level by these substrates was associated with electron trasnport and oxidative phosphorylation. α-Ketoacid inhibited pyruvate reduction to lactate in the lactate dehydrogenase (LDH) reaction, but increased pyruvate oxidation to CO2 . The NADH level in spermatids was too low to be detectable, but the NAD level remained unchanged in the presence of pyruvate and α-ketovalerate. These results suggest that pyruvate by itself is not an adequate energy-yielding substrate for spermatids and that a high NADH/NAD ratio may be essential for maintenance of their ATP level.