Eklund H
Pharmacol Biochem Behav. 1983;18 Suppl 1:73-81. doi: 10.1016/0091-3057(83)90150-8.
Alcohol dehydrogenase from horse liver has been thoroughly investigated with crystallographic methods. Four different crystal forms of the enzyme have been solved and refined. They show that the enzyme exists in two predominant forms. The open form is found in the absence of coenzyme and has two long deep clefts cutting the enzyme in three units. In the closed form of the enzyme these clefts are closed around the coenzyme and substrate/inhibitor. Although there are large conformational changes in the enzyme, they are mainly restricted to relative movements of the separate domains. The internal structure of these domains is virtually identical in the open and closed forms. The coenzyme is the main cause of the conformational change and binds with a large number of interactions to the enzyme. About 4% of the enzyme surface is covered by the bound coenzyme. The nicotinamide ring is not bound to the active site zinc atom, but puts one surface of the ring in contact with the zinc coordinated cysteine sulphur atoms. The oxygen atom of the substrate binds directly to the zinc atom with the rest of the substrate close to the nicotinamide of the coenzyme. Large substrates extend into a 15-20 A long hydrophobic channel which opens up towards the solution. The widely used inhibitor pyrazole binds as a bridge between the zinc atom and the nicotinamide ring. Pyrazoles substituted in the 4-position are generally strong inhibitors. This can be properly related to the organization of the substrate channel of the enzyme.
马肝醇脱氢酶已通过晶体学方法进行了深入研究。该酶的四种不同晶体形式已得到解析和优化。结果表明，该酶以两种主要形式存在。开放形式存在于无辅酶的情况下，有两条长而深的裂缝将酶切割成三个单元。在酶的封闭形式中，这些裂缝围绕辅酶和底物/抑制剂闭合。尽管酶存在较大的构象变化，但主要局限于各个结构域的相对移动。这些结构域的内部结构在开放和封闭形式中几乎相同。辅酶是构象变化的主要原因，并通过大量相互作用与酶结合。约4%的酶表面被结合的辅酶覆盖。烟酰胺环不与活性位点的锌原子结合，而是使环的一个表面与锌配位的半胱氨酸硫原子接触。底物的氧原子直接与锌原子结合，底物的其余部分靠近辅酶的烟酰胺。大的底物延伸到一个15 - 20埃长的疏水通道中，该通道向溶液开放。广泛使用的抑制剂吡唑作为锌原子和烟酰胺环之间的桥梁结合。在4位被取代的吡唑通常是强抑制剂。这可以与酶的底物通道的结构合理相关。
