3-Hydroxy-3-methyl-glutaryl-CoA reductase in Trypanosoma (Schizotrypanum) cruzi: subcellular localization and kinetic properties

Utilization of leucine and acetate as carbon sources for sterol and fatty acid biosynthesis by Old and New World Leishmania species, Endotrypanum monterogeii and Trypanosoma cruzi

The relative roles of acetate and leucine in the provision of a carbon source for fatty acid and sterol biosynthesis in several trypanosomatid species were investigated using 14C- and 13C-labelled acetate, glucose and leucine as substrates. Promastigotes of Leishmania species synthesized a large proportion of their sterol from leucine. L. major (LV39), L. amazonensis and L. mexicana were the most efficient utilizers of leucine, producing at least 70-77% of their sterol from leucine; L. braziliensis, L. donovani and L. tropica apparently produced less sterol from leucine (23-36%) and L. major (LV561), L. adleri and L. panamamensis were intermediate, utilizing leucine to provide 51-58% of their sterol. In all the cases the balance of the sterol produced was apparently synthesized from carbon arising from acetate. The related trypanosomatid Endotrypanum monterogeii also produced a large amount (77%) of its sterol from leucine rather than acetate. By contrast Trypanosoma cruzi elaborated only 8% of its sterol from leucine and used acetate far more effectively than the Leishmania species for sterol biosynthesis. The fatty acid moieties of the triacylglycerols and phospholipids were produced from acetate. Leucine was also incorporated into the fatty acids to varying extents in the different organisms showing that leucine can also be metabolized in trypanosomatids to generate acetyl-CoA.

Purification, localisation and characterisation of glucose-6-phosphate dehydrogenase of Trypanosoma brucei

Cell-fractionation and digitonin titration of procyclic trypomastigotes of Trypanosoma brucei, revealed that almost half of the total NADP+ -dependent glucose-6-phosphate dehydrogenase (G6PDH) activity, the first enzyme of the pentose phosphate pathway (PPP), is associated with glycosomes. The specific activity of G6PDH in the purified organelles was increased 4-fold relative to a total cell extract and showed latency. Moreover, in the absence of detergents this activity was totally resistant to the action of trypsin. The cytosolic counterpart was neither latent, nor was it resistant to trypsin. Both cytosolic and glycosomal G6PDH activities behaved identically on phenyl-, CM-, heparin-, and Affigel-blue-Sepharose columns. Both isoenzymes had a subunit Mr of 62 000 and an isoelectric point of 6.85, while kinetic studies carried out on the partially purified G6PDH from both cell compartments did not reveal any differences. The purified enzyme had an apparent Km of 138 and 5.3 microM for glucose 6-phosphate (G6P), and for NADP+, respectively, and had a specific activity of 14 micromol. (min mg of protein)(-1). We conclude that while in procyclic stages of T. brucei G6PDH activity is present in two different cell compartments, i.e. the cytosol and the glycosomes, these two activities most likely represent one and the same isoenzyme.