Orbital steering in the catalytic power of enzymes: Small structural changes with large catalytic consequences
Orbital steering in the catalytic power of enzymes: Small structural changes with large catalytic consequences
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DOI：
10.1126/science.277.5323.202
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发表时间：
1997-07-11
期刊：
影响因子：
56.9
通讯作者：
Koshland, DE
中科院分区：
文献类型：
--
作者：
Mesecar, AD;Stoddard, BL;Koshland, DE
对异柠檬酸脱氢酶（IDH）进行了微小的结构扰动，以评估精确的底物排列对酶催化能力的贡献。在以下两种情况下改变了IDH的反应轨迹：（i）将烟酰胺腺嘌呤二核苷酸磷酸的腺嘌呤部分变为次黄嘌呤（将6 - 氨基变为6 - 羟基）；（ii）用具有八个配位配体的Ca²⁺取代具有六个配位配体的Mg²⁺。这两种变化都使反应速度发生了较大（10⁻³到10⁻⁵）的改变，但通过对有活性的IDH复合物进行低温晶体学捕获发现，底物的取向（距离和角度）只有微小变化。这些结果提供了证据，表明由反应轨道的最佳取向产生的轨道重叠在酶的催化能力中起主要的定量作用。
Small structural perturbations in the enzyme isocitrate dehydrogenase (IDH) were made in order to evaluate the contribution of precise substrate alignment to the catalytic power of an enzyme. The reaction trajectory of IDH was modified (i) after the adenine moiety of nicotinamide adenine dinucleotide phosphate was changed to hypoxanthine (the 6-amino was changed to 6-hydroxyl), and (ii) by replacing Mg2+, which has six coordinating ligands, with Ca2+, which has eight coordinating ligands. Both changes make large (10(-3) to 10(-5)) changes in the reaction velocity but only small changes in the orientation of the substrates (both distance and angle) as revealed by cryocrystallographic trapping of active IDH complexes. The results provide evidence that orbital overlap produced by optimal orientation of reacting orbitals plays a major quantitative role in the catalytic power of enzymes.