Bryant C
Division of Biochemistry and Molecular Biology, Australian National University, Canberra.
Int J Parasitol. 1994 Dec;24(8):1089-97. doi: 10.1016/0020-7519(94)90184-8.
The characteristic respiratory metabolism of parasites consists of fermentation to carbon-rich, highly reduced volatile fatty acids which are excreted, and electron transport systems emphasising fumarate reductase and b-type cytochromes. The taxonomic groups that contribute major parasites (the heterogeneous protozoa and the helminths) have their evolutionary origins in environments from which oxygen was absent or present in very low concentrations. The Ediacarian period, about 700 million years ago, contains fossils of the appropriate grade of organisation to be contemporaneous with the ancestors of platyhelminths, nematodes and acanthocephalans. With the oxygen transition, carbon flow in the biosphere resulted in conservative, anoxic environments together with oxygen rich ones. The organisms of the former retained their emphasis on anaerobic energy generation, while cytochrome systems were as much concerned with oxygen detoxification as energy generation. Metabolic pathways in the modern parasitic groups are echoes of such ancient biochemistries.
寄生虫独特的呼吸代谢包括发酵产生富含碳的、高度还原的挥发性脂肪酸并排出体外，以及强调延胡索酸还原酶和b型细胞色素的电子传递系统。构成主要寄生虫类群（异质原生动物和蠕虫）的分类群在无氧或氧浓度极低的环境中起源进化。约7亿年前的埃迪卡拉纪时期含有与扁形虫、线虫和棘头虫祖先同时代的合适组织水平的化石。随着氧气转变，生物圈中的碳流产生了保守的缺氧环境和富氧环境。前者的生物仍侧重于厌氧能量产生，而细胞色素系统在能量产生的同时也同样关注氧气解毒。现代寄生类群的代谢途径就是这种古老生物化学的回响。
