Brändén C I, Eklund H
Ciba Found Symp. 1977(60):63-80. doi: 10.1002/9780470720424.ch5.
The apoenzyme and holoenzyme structures of liver alcohol dehydrogenase have been determined by X-ray methods to obtain details about coenzyme binding, substrate specificity and the catalytic mechanism. Coenzyme binding induces a conformational change of the protein which partly shields the active site from the solution. The reduced coenzyme binds in an open conformation similar to that of NAD bound to malate dehydrogenase. A hydrogen bond between Thr-178 and the carboxamide group of the coenzyme is essential for proper positioning of the nicotinamide in the active site. Coenzyme analogues in which the carboxamide group is absent or substituted with iodine bind in a different conformation and do not induce the structural change of the protein. Binding of substrate molecules has been studied in crystals obtained from an equilibrium mixture of enzyme, coenzyme and p-bromobenzyl alcohol. The oxygen atom of this substrate as well as that of the inhibitor molecules trifluoroethanol and dimethyl sulphoxide bind directly to the catalytic zinc atom. The substrate-binding region is a deep hydrophobic pocket at the bottom of which the zinc atom mediates electrophilic catalysis of alcohol oxidation.
已通过X射线方法确定了肝脏乙醇脱氢酶的脱辅酶和全酶结构，以获取有关辅酶结合、底物特异性和催化机制的详细信息。辅酶结合会引起蛋白质的构象变化，该变化部分地将活性位点与溶液隔离开来。还原型辅酶以类似于与苹果酸脱氢酶结合的NAD的开放构象结合。苏氨酸-178与辅酶的羧酰胺基团之间的氢键对于烟酰胺在活性位点的正确定位至关重要。缺少羧酰胺基团或被碘取代的辅酶类似物以不同的构象结合，并且不会诱导蛋白质的结构变化。已在由酶、辅酶和对溴苄醇的平衡混合物获得的晶体中研究了底物分子的结合。该底物的氧原子以及抑制剂分子三氟乙醇和二甲基亚砜的氧原子直接与催化锌原子结合。底物结合区域是一个深的疏水口袋，锌原子在其底部介导醇氧化的亲电催化。
