Cha Y, Murray C J, Klinman J P
Department of Chemistry, University of California, Berkeley 94720.
Science. 1989 Mar 10;243(4896):1325-30. doi: 10.1126/science.2646716.
Primary and secondary protium-to-tritium (H/T) and deuterium-to-tritium (D/T) kinetic isotope effects for the catalytic oxidation of benzyl alcohol to benzaldehyde by yeast alcohol dehydrogenase (YADH) at 25 degrees Celsius have been determined. Previous studies showed that this reaction is nearly or fully rate limited by the hydrogen-transfer step. Semiclassical mass considerations that do not include tunneling effects would predict that kH/kT = (kD/kT)3.26, where kH, kD, and kT are the rate constants for the reaction of protium, deuterium, and tritium derivatives, respectively. Significant deviations from this relation have now been observed for both primary and especially secondary effects, such that experimental H/T ratios are much greater than those calculated from the above expression. These deviations also hold in the temperature range from 0 to 40 degrees Celsius. Such deviations were previously predicted to result from a reaction coordinate containing a significant contribution from hydrogen tunneling.
已测定了在25摄氏度下，酵母醇脱氢酶（YADH）催化苄醇氧化为苯甲醛反应中，一级和二级氢-氚（H/T）以及氘-氚（D/T）动力学同位素效应。先前的研究表明，该反应几乎或完全受氢转移步骤的速率限制。不包括隧穿效应的半经典质量考量预测，kH/kT = (kD/kT)3.26，其中kH、kD和kT分别是氢、氘和氚衍生物反应的速率常数。现在已观察到一级效应尤其是二级效应均与该关系存在显著偏差，使得实验测得的H/T比值远大于根据上述表达式计算得出的值。这些偏差在0至40摄氏度的温度范围内也成立。先前预测这种偏差是由包含显著氢隧穿贡献的反应坐标导致的。
