Folate utilisation by Leishmania species and the identification of intracellular derivatives and folate-metabolising enzymes.

The use and metabolism of folates by leishmanias have been studied by assessing the growth of promastigotes in defined media with different folates and the cell content of folate-metabolising enzymes. The folates present in Leishmania mexicana mexicana have been determined using HPLC. Folic acid, 5-formyltetrahydrofolate (THF) and 5-methyl-THF each supported growth of L. m. mexicana promastigotes in defined medium, whereas the parasites did not survive in the absence of folates; p-aminobenzoic acid could not replace the folate requirement. The only folate present at detectable levels in L. m. mexicana promastigotes was 5-methyl-THF. Dihydrofolate reductase (EC 1.5.1.3), methylene-THF reductase (EC 1.1.1.68), serine hydroxymethyltransferase (EC 2.1.2.1) and thymidylate synthetase (EC 2.1.1.45) were all detected in extracts of promastigotes of L. m. mexicana, L. donovani and L. major. Some of these activities were also found in extracts of amastigotes of the former two species. The enzymes of L. m. mexicana have been partially characterised. Methylene-THF reductase may be involved in the conversion in vivo of 5-methyl-THF to 5,10-methylene-THF.