Activities of Glucose‐6‐phosphate, 6‐phosphogluconate, and Isocitrate Dehydrogenases from Leishmania donovani Cultivated at 25 and 37 C*

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Abstract
The activities of glucose-6-phosphate dehydrogenase (G-6-PD) (EC 1.1.1.49), 6-phosphogluconate dehydrogenase (PGD) (EC 1.1.1.44) and isocitrate dehydrogenase (ICD) (EC 1.1.1.42) from promastigotes of L. donovani strain 3S grown at 25.degree. C in modified Tobie''s (mT) medium and from promastigotes of the 37.degree. C-adapted substrain of this strain cultivated in the mT at 37.degree. C were assayed at 25.degree. and 37.degree. C. At 25.degree. C ICD from both the strain and the substrain had the highest, and PGD the lowest activity; the activity of G-6-PD was intermediate, but much closer to that of ICD. Irrespective of assay temperature the activities of G-6-PD and ICD from the 37.degree. C substrain were significantly higher than those of these enzymes from the parental strain, but the activity of PGD from the 25.degree. C strain was slightly higher than that of this dehydrogenase from the 37.degree. C-adapted stock. No significant activity losses of G-6-PD and ICD from either the strain or the substrain were noted after incubation of the extracts in the presence of 0.25 M sucrose at 37.degree. C for 2 h. PGD was unstable in such extracts, but it could be rendered stable by the addition of 4 mM 6-phosphogluconate. G-6-PD was the least and ICD the most dependent on Mg2+. In the 15-25.degree. C range, the Q10 values of the enzymes from the 25.degree. C strain were 2.83, 2.5 and 2.63 for G-6-PD, PGD and ICD, respectively. These values for the respective enzymes in the 25-35.degree. C range were 2.06, 1.67 and 1.62. The Q1O values of the enzymes from the 37.degree. C substrain in the 15-25.degree. C range were 2.06 for G-6-PD, 3.25 for PGD and 2.77 for ICD; in the 25-35.degree. C range, the corresponding values were 1.67, 1.46 and 1.83. Cultivation of the 37.degree. C substrain at 25.degree. C was accompanied by a drop in G-6-PD and ICD activities.