title: Lactate dehydrogenase isoenzymes of sperm cells and tests.
abstract: 1. The kinetic and metabolic properties of lactate dehydrogenase isoenzyme LDH(x) from human sperm cells and rat testes were studied. 2. LDH(x) shows a sensitivity to inhibition by stilboestrol diphosphate, urea and guanidinium chloride different from that of the LDH-H(4) and LDH-M(4) isoenzymes. 3. About 10 and 20% of the total lactate dehydrogenase activity of testes and sperm cells respectively were associated with particulate fractions. In sperm cells 11% was localized in the middle piece and 18.8% in the head fraction. LDH(x) was found in all particulate fractions of sperm cells. The middle piece contained 41.0% of total LDH(x) activity and showed high succinate dehydrogenase activity. 5. The pH-dependence of lactate/pyruvate and NAD(+)/NADH concentration ratios were estimated. Lactate dehydrogenase in sperm cells has maximal activity with NADH as coenzyme at pH7.5 and with NADPH as coenzyme at pH6.0. At pH6.0 a 10% greater oxidation of NADPH than of NADH was found. At acid pH lactate hydrogenase may function as an enzyme bringing about transhydrogenation from NADPH to NAD(+). 6. In agreement with the stoicheiometry of the lactate de- hydrogenase reaction, the lactate/pyruvate concentration ratio decreased with increasing pH. 7. The lactate/pyruvate and NAD(+)/NADH concentration ratios were estimated with glucose, fructose and sorbitol as substrates and as a function of time after addition of these substrates. During a 20min. period after the addition of the substrates, changes in lactate/pyruvate and NAD(+)/NADH concentration ratios were noticed. Increasing concentration of the substrates mentioned gave rise to asymptotic increases in lactate and pyruvate. 8. Sorbitol did not act as a substrate for LDH(x). 9. The findings described are consistent with the idea that LDH(x) is different from other known lactate dehydrogenase isoenzymes, but that it has a metabolic function similar to that of the isoenzymes of other tissues.
mesh_terms: D000818:Animals; D004054:Diethylstilbestrol / Q000494:pharmacology; D005632:Fructose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007773:Lactates / Q000378:metabolism; D008297:Male; D009243:NAD / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism; D051381:Rats; D012661:Semen / Q000201:enzymology*; D013012:Sorbitol / Q000378:metabolism; D013737:Testis / Q000201:enzymology*; D014508:Urea / Q000494:pharmacology
chemical_list: D007527:Isoenzymes; D007773:Lactates; D011773:Pyruvates; D009243:NAD; D005632:Fructose; D013012:Sorbitol; D004054:Diethylstilbestrol; D014508:Urea; D007770:L-Lactate Dehydrogenase; D005947:Glucose