Zaks A, Klibanov A M
Department of Applied Biological Sciences, Massachusetts Institute of Technology, Cambridge 02139.
J Biol Chem. 1988 Jun 15;263(17):8017-21.
Three model, unrelated enzymes (yeast alcohol oxidase, mushroom polyphenol oxidase, and horse liver alcohol dehydrogenase) were found to be catalytically active in a variety of organic solvents. For all enzymes and solvents tested, the enzymatic activity greatly increased upon an increase in the water content in the solvents (which always remained below the solubility limit). Much less water was required to reach the maximal activity in hydrophobic solvents than in their hydrophilic counterparts. However, when the catalytic activity was plotted versus the amount of water bound to the enzymes, a common pattern emerged for different solvents. These data suggest that the effect of organic solvents on an enzyme is primarily due to interactions with the enzyme-bound, essential layer of water rather than with the enzyme itself. At optimal water contents, enzymatic activities in organic solvents were in the range from 20 to 40% of those in aqueous solutions. From experiments on (i) replacement of water with other hydrogen bond-forming additives and (ii) titration of enzyme amino groups in an organic medium, as well as the literature data on dehydrated enzymes, it is concluded that the water required by enzymes in nonaqueous solvents provides them with sufficient conformational flexibility needed for catalysis.
研究发现，三种模式下、不相关的酶（酵母醇氧化酶、蘑菇多酚氧化酶和马肝醇脱氢酶）在多种有机溶剂中具有催化活性。对于所有测试的酶和溶剂，随着溶剂中水分含量的增加（始终保持在溶解度极限以下），酶活性大幅提高。与亲水性溶剂相比，疏水性溶剂达到最大活性所需的水量要少得多。然而，当将催化活性与结合到酶上的水量作图时，不同溶剂呈现出共同的模式。这些数据表明，有机溶剂对酶的影响主要是由于与酶结合的必需水层相互作用，而非与酶本身相互作用。在最佳含水量下，有机溶剂中的酶活性为水溶液中酶活性的20%至40%。通过（i）用其他形成氢键的添加剂替代水以及（ii）在有机介质中滴定酶氨基的实验，以及关于脱水酶的文献数据，得出结论：非水溶剂中酶所需的水为它们提供了催化所需的足够构象灵活性。
