Hitchings G H
Adv Enzyme Regul. 1982;20:375-86. doi: 10.1016/0065-2571(82)90026-7.
Protozoa possess a wealth of purine-salvage enzymes, many with unique, or unusual, substrate specificities. As a result, many opportunities for the chemotherapist exist. An exemplification is found in the conversion in schistosomes of allopurinol ribonucleoside to the corresponding ribonucleotide followed by further anabolism to the very toxic 4-aminopyrazolo(3,4-d)pyrimidine 1-ribonucleotide. The same organisms convert another inosine analog, formycin B, to the ribonucleotide, but its inhibitory effects appear to be exercised primarily by inhibition of the organism's adenylosuccinate synthase. A substantial segment of the Phylum Protozoa shows no vestigial traces of ability to synthesize purines de novo although thymidylate synthase appears to be present in many. The absence of other tetrahydrofolate catalyzed reactions suggests that these functions were never acquired.
原生动物拥有大量嘌呤补救酶，其中许多具有独特或不寻常的底物特异性。因此，化疗师有很多机会。一个例子是在血吸虫中，别嘌呤醇核糖核苷转化为相应的核糖核苷酸，随后进一步合成代谢为毒性很强的4-氨基吡唑并（3,4-d）嘧啶1-核糖核苷酸。同样的生物体将另一种肌苷类似物，间型霉素B，转化为核糖核苷酸，但其抑制作用似乎主要是通过抑制生物体的腺苷酸琥珀酸合酶来实现的。相当一部分原生动物门没有从头合成嘌呤的残留能力，尽管许多原生动物中似乎存在胸苷酸合酶。其他四氢叶酸催化反应的缺失表明这些功能从未获得。
