LEVELS OF CERTAIN SOLUBLE DEHYDROGENASES IN THE RAT TESTIS AND EPIDIDYMIS

Abstract

Reduced nicotinamide-adenine dinucleotide phosphate (NADPH), required as co-factor for lipogenesis and steroidogenesis, may, in part, be supplied by pyridine nucleotide transhydrogenation mediated by malate dehydrogenase (oxaloacetate+NADH→malate+NAD) and the malate (`malic') enzyme (malate+NADP→pyruvate+CO2+NADPH). The malate transhydrogenation reactions (cf. Ballard & Hanson, 1967, for references) are apparently of some importance in luteinized rat ovaries in which glucose-6-phosphate dehydrogenase is by far exceeded in activity by the malate enzyme (Lunaas & Baldwin, 1967). In rat testes high activities of the malate enzyme and of isocitrate dehydrogenase were reported by Brown, McLean & Greenbaum (1966). We have confirmed these findings (Table 1). In addition we determined glucose-6-phosphate dehydrogenase, 6-phospho-gluconate dehydrogenase and the NAD(H)-dependent malate dehydrogenase. Remarkably low levels were consistently obtained for glucose-6-phosphate dehydrogenase, the apparent activity of this enzyme in the testes being even lower than