Transformation of Uroporphyrinogen III into Protohaem
Transformation of Uroporphyrinogen III into Protohaem
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DOI：
10.1007/978-0-387-78518-9_4
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发表时间：
2009
期刊：
影响因子：
--
通讯作者：
Johanna E. Cornah;Alison G. Smith
中科院分区：
文献类型：
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作者：
Johanna E. Cornah;Alison G. Smith
血红素是几乎所有生物体的重要辅助因子。它由四吡咯的共同祖先尿卟啉原III通过四种连续的酶制成：尿卟啉原III脱羧酶，粪卟啉原III氧化酶，原卟啉原IX氧化酶和亚铁螯合酶。每一种酶都催化一个显著的反应，前三种酶需要在底物分子上的多个位点进行相同的反应。现在，晶体结构可用于每种蛋白质，这些基本酶的机制开始被阐明。尽管血红素合成的普遍性，但是生物体之间存在差异。首先，在许多细菌中存在两种氧化酶的厌氧形式，它们似乎与真核生物中发现的需氧形式具有完全不同的起源。其次，在某些细菌中，这些酶中的一些或全部完全缺失;它们要么是致病性的，可以从其宿主中摄取血红素，要么存在替代的、尚未表征的酶。最后，在真核生物中，酶的亚细胞分布因生物体而异，这对生物合成途径的调节有影响。
Haem is an essential cofactor for virtually all organisms. It is made from the common tetrapyrrole progenitor, uroporphyrinogen III, by four sequential enzymes: uroporphyrinogen III decarboxylase, coproporphyrinogen III oxidase, protoporphyrinogen IX oxidase, and ferrochelatase. Each of the enzymes catalyses a remarkable reaction, with the first three required to carry out the same reaction at multiple sites on the substrate molecule. Now that the crystal structures are available for each of the proteins, the mechanisms of these essential enzymes are beginning to be elucidated. Despite the universality of haem synthesis however, there are differences between organisms. Firsdy in many bacteria there are anaerobic forms of the two oxidases, which appear to have completely different origins from the aerobic forms found in eukaryotes. Secondly, in certain bacteria some or all of these enzymes are missing completely; either they are pathogenic and can take up haem from their host, or there are alternative, as yet uncharacterized, enzymes. Finally, within the eukaryotes, the subcellular distribution of the enzymes differs depending on the organism, which has ramifications for the regulation of the biosynthetic pathway.