Scott D A, Coombs G H, Sanderson B E
Mol Biochem Parasitol. 1987 Mar;23(2):139-49. doi: 10.1016/0166-6851(87)90149-6.
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.
通过评估前鞭毛体在含有不同叶酸的特定培养基中的生长情况以及叶酸代谢酶的细胞含量，对利什曼原虫中叶酸的利用和代谢进行了研究。已使用高效液相色谱法测定了墨西哥利什曼原虫中的叶酸。叶酸、5-甲酰四氢叶酸（THF）和5-甲基-THF均可支持墨西哥利什曼原虫前鞭毛体在特定培养基中的生长，而在没有叶酸的情况下，寄生虫无法存活；对氨基苯甲酸不能替代对叶酸的需求。在墨西哥利什曼原虫前鞭毛体中可检测到的唯一叶酸是5-甲基-THF。在墨西哥利什曼原虫、杜氏利什曼原虫和硕大利什曼原虫前鞭毛体提取物中均检测到二氢叶酸还原酶（EC 1.5.1.3）、亚甲基-THF还原酶（EC 1.1.1.68）、丝氨酸羟甲基转移酶（EC 2.1.2.1）和胸苷酸合成酶（EC 2.1.1.45）。在上述前两个物种的无鞭毛体提取物中也发现了其中一些活性。已对墨西哥利什曼原虫的这些酶进行了部分表征。亚甲基-THF还原酶可能参与体内5-甲基-THF向5,10-亚甲基-THF的转化。
