Subcellular localization of branched-chain amino acid aminotransferase and lactate dehydrogenase C4 in rat and mouse spermatozoa

Abstract

Spermatozoa isolated from rat and mouse epididymes show a relatively high branched-chain amino acid aminotransferase (leucine aminotransferase, EC 2.6.1.6) activity. There is a significant reduction of leucine aminotransferase and of the isoenzyme C4 of lactate dehydrogenase (EC 1.1.1.27) in the gametes during their epididymal transit. Studies of patterns of liberation of the leucine aminotransferase and of the lactate dehydrogenase C4 from intact spermatozoa, treated with increasing concentrations of digitonin, indicate that both enzymes have the same dual subcellular location, i.e. in the cytosol and in the mitochondria.

Trypanosoma cruzi: inhibition of alpha-hydroxyacid dehydrogenase isozyme II by N-allyl and N-propyl oxamates and their effects on intact epimastigotes

“…Enzyme assays -HADH-isozyme II activity was determined using α-ketoisocaproate as substrate (Montamat et al 1988). The reagent mixture contained, in a final volume of 3 ml: 0.12 mM NADH, 0.1 M sodium phosphate buffer pH 7.4, α-ketoisocaproate as neutral sodium salt (concentrations indicated in results), enzyme preparation, properly diluted with 0.1 M sodium phosphate buffer pH 7.4 in order to obtain an absorbance change at 340 nm of 0.05-0.08 per min with a 5 mM concentration of substrate.…”

“…On the contrary isozyme II does not show activity against pyruvate and it is active on a broad of linear and branched chain substrates specially α-ketocaproate and α-ketoisocaproate (Coronel et al 1981). It is interesting that HADH-isozyme II found in T. cruzi, shows a substrate spectrum similar to that of LDH-C4 (Coronel et al 1981, Montamat et al 1988, suggesting that this HADH- isozyme II may also accomplish very specific functions in T. cruzi (Montamat et al 1987). On account of the similarities between HADH-isozyme II and LDH-C4, it has been proposed that these isozymes are functionally homologous (Coronel et al 1981, Montamat et al 1987, 1988 and they must be integrated in metabolic pathways supplying energy for the motility of flagellum and survival of the parasite (Coronel et al 1981, Montamat et al 1987 or the spermatozoa, respectively (Coronel et al 1986).…”

Differences in ATP Generation Via Glycolysis and Oxidative Phosphorylation and Relationships with Sperm Motility in Mouse Species

“…Regardless of whether lactate (51)(52)(53) or pyruvate (18,34,54) is the primary respiratory substrate entering mouse sperm mitochondria, the composition of the medium used in our experiments made active glycolysis a prerequisite for OXPHOS. Although the physiological (in vivo) relevance of the uptake by mitochondria of glycolytic products excreted by the principal piece is uncertain, the different regions of the mouse female reproductive tract (vagina, uterus, and oviduct) present relatively high lactate/glucose ratios around the time of ovulation (2, 7) that would enable sperm to import sufficient exogenous lactate to fuel OXPHOS (52,53,55,56).…”

“…Although the physiological (in vivo) relevance of the uptake by mitochondria of glycolytic products excreted by the principal piece is uncertain, the different regions of the mouse female reproductive tract (vagina, uterus, and oviduct) present relatively high lactate/glucose ratios around the time of ovulation (2, 7) that would enable sperm to import sufficient exogenous lactate to fuel OXPHOS (52,53,55,56). Furthermore, when sperm are suspended in seminal plasma, fructose is by far the main metabolic substrate (2).…”

Inhibition ofTrypanosoma cruziα-Hydroxyacid Dehydrogenase-isozyme II by N-Isopropyl Oxamate and its Effect on Intact Epimastigotes

“…4 Isozyme I is responsible for the weak lactate dehydrogenase activity found in T. cruzi extracts, 5 while isozyme II does not show activity against pyruvate 6 and is active on a broad spectrum of linear and branched chain substrates, specially a-ketoisocaproate. 6 Since T. cruzi HADH-isozyme II shows a substrate specificity similar to that of LDH-C4, 6,7 it is probably that HADH-isozyme II may accomplish similar functions in T. cruzi 8 to those ascribed to LDH-C4 in mammalian spermatozoa. On account of the similarities between HADH-isozyme II and LDH-C4, it has been proposed that these enzymes must be integrated in metabolic pathways supplying energy for the motility of flagellum and survival of the parasite, 6,8 or the spermatozoa respectively.…”