The ontogeny of sperm specific lactate dehydrogenase in mice

Testes of sexually mature mice (Mus musculus) contain a unique lactate dehydrogenase isozyme associated with the spermatozoan cell. This isozyme differs in subunit composition and reactivity to the substrate DL‐α‐hydroxyvalerate when compared to the usual five isozymes found in other tissues. It has been termed LDH‐X and has the same mobility as LDH‐5 when subjected to electrophoresis on standard polyacrylamide gels. This enzyme first appears during development at the time spermatocytes first mature in the testes. From the time of birth until sexual maturity is reached the specific activity of LDH in testes extracts does not change appreciably. When the mice have reached the weight of 6.5 to 7.5 g with a testes weight of 20 mg, which is equivalent to an age of 15 to 17 days postpartum, LDH‐X appears. It is at approximately this time that the first differentiative division of the primitive germ cell, the spermatogonium, occurs. For the next period of time, 15–20 days, the testes grow and differentiate at a rapid rate and during this same period the specific activity of the sperm LDH also increses. Histochemical evidence indicated that activity of LDH‐1, 2, and 3 is highest in the interstitial cells while LDH‐X activity is restricted to the cells that are close to the lumen of the testicular tubule.