PURINE/PYRIMIDINE METABOLISM IN TRICHOMONAS AND GIARDIA

三种厌氧菌寄生虫，贾第鞭毛虫，阴道毛滴虫 和胎儿三毛滴虫，它们都是通过附着在宿主上自然生长的 上皮细胞和执行吞噬作用，已经发现缺乏 嘌呤和嘧啶核苷酸从头合成的能力， 缺乏二氢叶酸还原酶和胸苷酸合成酶 活动 它们依赖于相当简单的嘌呤补救途径， 嘧啶和核苷。 这些路径，由我们描绘在 在过去的两年里，已经提出了几个关键的酶，不仅是 对这些寄生虫的生存至关重要， 特异性使其自身成为抗寄生虫药的潜在靶点 化疗 这些酶是G.兰布利亚， HXGPRT、UPRT和IMPDH在T.胎儿和脱氧核糖核苷 磷酸转移酶流浪汉 GPRT、HXGPRT和IMPDH已经 纯化到均匀，并显示出许多不同的性质， 相关的宿主酶。 我们正在计划一个筛选项目， 这些分离酶的抑制剂作为发现化疗药物的一种方式 剂. 另一方面，我们将制备G. Lamblia GPRT， T. fetus HXGPRT、T.胎儿IMPDH和小鼠肉瘤180 IMPDH（微克） 数量按既定程序。 的N-末端序列。 将测定四种纯化的酶， 寡核苷酸将被合成并用作探针以开始 编码这些基因的鉴定、克隆和测序 用于序列比较的酶。 据预测， 与酶活性位点相关的差异可以解释 不同的底物特异性，并帮助新的药物设计。 同时， UPRT和T的进一步纯化。阴道毛 脱氧核糖核苷磷酸转移酶将用亲和柱 色谱法。 一个令人兴奋的观察， T. vagulovirus的发现，T. 迷走神经DNA和RNA之间的可能关系， T.流浪汉会带领我们进一步追踪 这些新的发现。 T.流浪汉将是 建立和双链RNA将被用作探针，以启动 其编码区的鉴定、克隆和序列测定 基因组，以进一步了解的生物学功能， 双链RNA

Three anaerobic protozoan parasites, Giardia Lamblia, Trichomonas vaginalis and Tritrichomonas foetus, which all grow naturally by adhering to host epithelial cells and performing phagocytosis, have been found lacking the capability of de novo synthesis of purine and pyrimidine nucleotides and deficient in dihydrofolate reductase and thymidylate synthetase activities. They depend on rather simple salvage pathways for purines, pyrimidines and nucleosides. These pathways, delineated by us during the past two years, have presented several pivotal enzymes which not only are essential for survival of these parasites but also exhibit unique substrate specificities qualifying themselves as potential targets of antiparasitic chemotherapy. These enzymes are the APRT, GPRT and UPRT in G. lamblia, HXGPRT, UPRT and IMPDH in T. foetus and the deoxyribonucleoside phosphotransferase of T. vaginalis. The GPRT, HXGPRT and IMPDH have been purified to homogeneity and shown to have many different properties from the related host enzymes. We are planning on a screening program for inhibitors of these isolate enzymes as one way of finding chemotherapeutic agents. On the other hand we will prepare pure samples of G. lamblia GPRT, T. foetus HXGPRT, T. foetus IMPDH and mouse sarcoma 180 IMPDH in microgram quantities by the established procedures. The N-terminal sequences of the four purified enzymes will be determined, the corresponding oligonucleotides will be synthesized and used as probes to begin identifications, clonings and sequencings of the genes encoding these enzymes for sequence comparisons. It is anticipated that sequence differences associated with the enzyme active sites may explain the different substrate specificities and help new drug designs. Meanwhile, further purifications of the UPRT's and the T. vaginalis deoxyribonucleoside phosphotransferase will be pursued with affinity column chromatographies. An exciting observation of the presence of a double-stranded RNA in T. vaginalis, the discovery of the RNA gene in T. vaginalis DNA and the possible relationship between the RNA and the metronidazole-sensitivity of T. vaginalis will lead us into further pursue of these new findings. Genomic libraries of T. vaginalis will be established and the double-stranded RNA will be used as a probe to initiate the identification, cloning and sequence determination of its encoding genome for further understanding of the biological function of the double-stranded RNA.