Xu Z F, Larreta-Garde V, Thomas D
Laboratoire de Technologie Enzymatique, Université de Technologie de Compiègne, France.
Biochim Biophys Acta. 1989 Oct 19;998(3):251-7. doi: 10.1016/0167-4838(89)90281-1.
Sorbitol, added as a depressor of water activity in the reaction medium of yADH, can modify the kinetic behaviour of the enzyme towards the four substrates tested: ethanol, propanol, butanol and pentanol, as well as towards the coenzyme NAD. All apparent Km values of the alcohol substrates and NAD decreased as the additive concentration increased. However, the additive-caused modifications of the enzyme activity were found to depend on the carbon-chain length of the alcohol substrate, in other words, the catalytic selectivity of the enzyme towards different substrates was changed by the additive. These results and supplementary experiments suggested that sorbitol may have two opposing effects on the enzyme: the positive effect leads the enzyme to adopt a conformation which is more accessible to its substrates; while the negative effect results in a diffusional constraint for the enzyme reaction. Observed results were the combination of the two opposing effects.
山梨醇作为酵母乙醇脱氢酶（yADH）反应介质中水活度的抑制剂，可改变该酶对所测试的四种底物（乙醇、丙醇、丁醇和戊醇）以及辅酶NAD的动力学行为。随着添加剂浓度的增加，所有醇类底物和NAD的表观米氏常数（Km）值均降低。然而，发现添加剂引起的酶活性变化取决于醇类底物的碳链长度，换句话说，添加剂改变了酶对不同底物的催化选择性。这些结果及补充实验表明，山梨醇可能对该酶有两种相反的作用：正向作用使酶采取对其底物更易接近的构象；而负向作用导致酶反应的扩散限制。观察到的结果是这两种相反作用的综合。
