Secondary .beta.-deuterium isotope effects in decarboxylation and elimination reactions of .alpha.-lactylthiamin: intrinsic isotope effects of pyruvate decarboxylase
作者:Ronald. Kluger、Michael. Brandl
DOI:10.1021/ja00284a056
日期:1986.11
enzymic reaction. 2-(Lact-2-yl-..beta..-d/sub 3/) thiamine was prepared by condensation of methyl pyruvate-d/sub 3/ with thiamine followed by hydrolysis. The isotope effect for decarboxylation of lactylthiamin in acidic solution at 25/sup 0/C (k/sub H3//k/sub D3/) is 1.09 (standard deviation (SD) 0.015) in pH 3.8, 0.5 M sodium acetate: isotope effect = 1.095 (SD 0.014) in 0.001 M HCl. The reaction was
丙酮酸和硫胺素的加合物,乳基硫胺素(2-(乳酸-2-基)硫胺素)的反应是丙酮酸脱羧酶催化过程中形成的中间体反应的准确非酶模型。酶促反应从丙酮酸和硫胺二磷酸生成乳基硫胺二磷酸。..β..-氘同位素效应对非酶促反应进行测定,结果与同位素对酶促反应的影响有关。2-(Lact-2-yl-..beta..-d/sub 3/)硫胺是通过丙酮酸甲酯-d/sub 3/与硫胺缩合然后水解制备的。在 25/sup 0/C (k/sub H3//k/sub D3/) 的酸性溶液中,乳酸硫胺脱羧的同位素效应为 1.09(标准偏差 (SD) 0.015),pH 3.8,0.5 M 醋酸钠:同位素效果 = 1.095 (SD 0.014) 在 0.001 M HCl 中。还使用 38% 乙醇醋酸钠水溶液(在与乙醇混合之前 pH 值为 3.8)研究了该反应,因为酶位点的极性低于水,并且共溶剂显着加速了反应。同位素效应在水中反应的统计范围内,1