Avila J L, Polegre M A
Instituto de Biomedicina, Caracas, Venezuela.
Mol Biochem Parasitol. 1993 Mar;58(1):123-34. doi: 10.1016/0166-6851(93)90096-g.
Promastigotes of Leishmania mexicana and Leishmania braziliensis incorporate S-adenosyl-L-[3H-methyl]methionine (AdoMet) against a concentration gradient through a saturable system. This concentrative uptake requires metabolic energy and is sensitive to temperature and sulfhydryl reagents such as N-ethyl maleimide. Intracellular AdoMet exchanges with external AdoMet. At steady state, unaltered ADoMet in the intracellular pool is at about a 1800-fold concentration in relation to that found in the external medium. Glucose, galactose and ribose did not stimulate uptake rates. Incorporated AdoMet goes into the soluble AdoMet pool, where a small fraction is metabolized, chiefly into methylthioadenosine, decarboxylated AdoMet and methanol. After a 60 min pulse the radioactivity associated with the [3H]AdoMet incorporated disappears with a half-time of 2 h. Transmethylation reactions were analyzed following [3H]AdoMet incorporation. Fractionation experiments indicate that 45-62% and 30-42% of the radioactivity is incorporated into lipids and protein methyl esters respectively, with 5-14% present in the soluble pool of parasites. Sinefungin or its cyclic derivative (1 and 10 micrograms ml-1) in the incubation medium produces 58% and 64% inhibition of AdoMet incorporation into Leishmania promastigotes. Most transmethylation reactions are inhibited, as there is a 50% decrease in the total radioactivity present in both the base-labile and lipidic fraction, with a parallel increase in the percentage of radioactivity in the soluble pool. Previous results give evidence of the importance of AdoMet in American Leishmania promastigote metabolism.
墨西哥利什曼原虫和巴西利什曼原虫的前鞭毛体通过一个可饱和系统逆浓度梯度摄取S-腺苷-L-[3H-甲基]甲硫氨酸（AdoMet）。这种浓缩摄取需要代谢能量，并且对温度和巯基试剂（如N-乙基马来酰亚胺）敏感。细胞内的AdoMet与细胞外的AdoMet进行交换。在稳态时，细胞内池未改变的AdoMet浓度相对于细胞外培养基中的浓度约为1800倍。葡萄糖、半乳糖和核糖不会刺激摄取速率。摄取的AdoMet进入可溶性AdoMet池，其中一小部分被代谢，主要代谢为甲硫基腺苷、脱羧AdoMet和甲醇。经过60分钟的脉冲后，与摄取的[3H]AdoMet相关的放射性以2小时的半衰期消失。在[3H]AdoMet摄取后分析转甲基反应。分级分离实验表明，分别有45 - 62%和30 - 42%的放射性掺入脂质和蛋白质甲酯中，5 - 14%存在于寄生虫的可溶性池中。在孵育培养基中加入西奈芬净或其环状衍生物（1和10微克/毫升）可分别抑制58%和64%的AdoMet掺入利什曼原虫前鞭毛体。大多数转甲基反应受到抑制，因为碱基不稳定部分和脂质部分中存在的总放射性降低了50%，同时可溶性池中放射性的百分比相应增加。先前的结果证明了AdoMet在美洲利什曼原虫前鞭毛体代谢中的重要性。
