Weitzman P D
Department of Biochemistry, University of Bath, U. K.
Biochem Soc Symp. 1987;54:33-43.
The citric acid cycle performs a dual role in cell metabolism, acting as a source of both 'energy' and biosynthetic starting materials. The widespread occurrence of the cycle throughout Nature is an excellent example of the unity of biochemistry, but closer examination reveals that there is considerable diversity in the citric acid cycle of different organisms with respect to metabolic role, molecular enzymology and mode of regulation. Two enzymes of the cycle--citrate synthase and succinate thiokinase--have been found to exhibit particularly striking patterns of diversity in structure and catalytic and regulatory function. Some of these patterns show a correlation with the taxonomic groupings of the organisms and with their physiological characteristics. Comparative enzyme studies have a contribution to make to an ultimate understanding of the cycle and its cellular operation, and there are substantial benefits to be gained from interactive studies on both prokaryotic and eukaryotic systems.
柠檬酸循环在细胞代谢中发挥着双重作用，既是“能量”来源，也是生物合成起始原料的来源。该循环在自然界广泛存在，是生物化学统一性的一个绝佳例子，但仔细研究发现，不同生物体的柠檬酸循环在代谢作用、分子酶学和调节方式方面存在相当大的差异。该循环中的两种酶——柠檬酸合酶和琥珀酸硫激酶——已被发现其结构、催化和调节功能呈现出特别显著的多样性模式。其中一些模式与生物体的分类群及其生理特征相关。比较酶学研究有助于最终理解该循环及其细胞运作过程，并且对原核生物和真核生物系统进行交互研究能带来诸多实质性益处。
