Temperature and metabolism in Leishmania: III. Some dehydrogenases of L. donovani, L. mexicana, and L. tarentolae

Abstract

The effects of temperature on four dehydrogenases in homogenates of promastigotes of Leishmania donovani (several strains), L. mexicana, and L. tarentolae were studied. Activities of isocitrate dehydrogenase (ICD) (EC 1.1.1.42), glyceraldehydephosphate dehydrogenase (GAPD) (EC 1.2.1.12), glucose-6-phosphate dehydrogenase (G-6-PD) (EC 1.1.1.49), and phosphogluconate dehydrogenase (PGD) (EC 1.1.1.44) were measured at temperatures from 25 C up to 45 C by following the reduction of nucleotide cofactors spectrophotometrically. Residual activities were measured at 25 C following incubation at 37 C for 30, 60, and 90 min. ICD, GAPD, and G-6-PD generally increased in initial activity over the temperature range, but activities and rates of increase varied according to enzyme, species, and strain. PGD activity decreased sharply over the investigated range in L. mexicana and all L. donovani strains, but increased in L. tarentolae. Residual activity curves confirmed the observed temperature-activity differences between L. tarentolae and the mammalian parasites with respect to PGD, and, in addition, showed that the ICD, GAPD, and G-6-PD of the cutaneous L. mexicana were more thermolabile than the same enzymes of the visceral L. donovani. The HM strain of L. donovani, which in hamsters produces infections of lower virulence than the other strains studied (Khartoum, 1S, 2S, 3S), also showed the lowest ICD, G-6-PD, and PGD activity over most of the temperature range.