SummaryIsocitrate dehydrogenase (ICDH), succinate dehydrogenase (SDH), malate dehydrogenase (MDH), glutamate dehydrogenase (GDH), β-hydroxybutyrate dehydrogenase (β-OH-BDH) and glucose-6-phosphate dehydrogenase (G-6-PDH) were histochemically located in the testes of buffaloes, goats and rams. The enzyme activities varied with the enzyme, species and cell type. The activities in the seminiferous tubules were correlated with the stages of seminiferous epithelial cycle (SEC). During this cycle, the activities in the Sertoli cells, spermatogonia and spermatocytes remained unaltered in contrast to those in the spermatids. The activities of SDH, ICDH and MDH were relatively greater in buffalo, while goat and ram resembled each other quite closely. ICDH and MDH preferred NADP to NAD. In the three species, the activities of ICDH, SDH and MDH generally followed an increasing order. G-6-PDH was greater in the interstitial tissue of buffalo than in goat and ram; the maximum activity of this enzyme in each species was found in the spermatogonia. In comparison with G-6-PDH, GDH was less evident in the interstitial tissue of buffalo and goat; Sertoli cells and spermatogonia also showed relatively less MDH activity whereas the other germ cells may have relatively less, similar or more, GDH activity depending on the species. β-OHBDH activity was similar in the interstitial tissue of the three species, but in the seminiferous tubule, the activity was less in goat. But for GDH and β-OH-BDH which could show different results, the activities of other enzymes generally decreased from spermatogonia through spermatocytes to spermatids but increased during spermiogenesis. In spermatozoa, the enzymes were observed only in the mid-piece. The possible physiological significance of the results is discussed in relation to different metabolic pathways.
The apparent Km is a misleading kinetic indicator
