Barrett J
Department of Biological Sciences, University College of Wales, Aberystwyth, UK.
Adv Parasitol. 1991;30:39-105. doi: 10.1016/s0065-308x(08)60306-1.
Amino acids are major constituents of biological material. Chemically they are extremely stable and combine a relatively simple molecular structure with a wide range of properties and functions. In general, amino acid metabolism in helminths has been relatively neglected and the information available is often uneven and of uncertain quality. However, the search for new target sites for anthelmintic development has led to a renewed interest in this area. The amino acid composition of helminths is similar to that of other invertebrates and no unique amino acids have been reported. With the possible addition of tyrosine, helminths seem to require the same 10 essential amino acids as mammals and, where studied in detail, the pathways of amino acid synthesis in helminths are similar to those of mammals. Although amino acids are not a significant energy source in parasites, helminths are able to catabolize amino acids by pathways which, again, appear identical to those found in mammals. Helminths have also been shown to carry out a number of oxidative reactions associated with amino acid metabolism, including cysteine dioxygenase, proline hydroxylase and tryptophan hydroxylase. There are, however, differences in detail between the pathways of amino acid metabolism in helminths and mammals, particularly in the metabolism of the sulphur amino acids and arginine and proline. These differences may be exploitable in anthelmintic design and proline analogues and proline biosynthesis inhibitors show some potential as fasciolicides (Sheers et al., 1982). Differences in metabolism between parasites and their hosts may be the result of parasitic adaptation or they may merely reflect general features of the invertebrate phyla as a whole. Thus a comparison of amino acid metabolism in parasitic helminths with that of their free-living relatives may give some insight into the biochemical basis of parasitism.
氨基酸是生物物质的主要成分。从化学角度来看，它们极其稳定，将相对简单的分子结构与广泛的特性和功能结合在一起。总体而言，蠕虫体内的氨基酸代谢相对受到忽视，现有信息往往参差不齐且质量不确定。然而，寻找抗蠕虫药物开发的新靶点引发了人们对该领域的新兴趣。蠕虫的氨基酸组成与其他无脊椎动物相似，尚未有独特氨基酸的报道。除了可能添加酪氨酸外，蠕虫似乎需要与哺乳动物相同的10种必需氨基酸，并且在详细研究的情况下，蠕虫体内氨基酸合成途径与哺乳动物的相似。虽然氨基酸不是寄生虫的重要能量来源，但蠕虫能够通过与哺乳动物中发现的途径相同的途径分解代谢氨基酸。蠕虫还被证明能进行一些与氨基酸代谢相关的氧化反应，包括半胱氨酸双加氧酶、脯氨酸羟化酶和色氨酸羟化酶。然而，蠕虫和哺乳动物的氨基酸代谢途径在细节上存在差异，特别是在含硫氨基酸以及精氨酸和脯氨酸的代谢方面。这些差异在抗蠕虫药物设计中可能具有可利用价值，脯氨酸类似物和脯氨酸生物合成抑制剂显示出作为杀片形吸虫剂的一些潜力（Sheers等人，1982年）。寄生虫与其宿主之间代谢的差异可能是寄生适应的结果，也可能仅仅反映了整个无脊椎动物门的一般特征。因此，将寄生蠕虫的氨基酸代谢与其自由生活的亲属进行比较，可能会深入了解寄生现象的生化基础。
