Holme E
Biochim Biophys Acta. 1982 Oct 5;707(2):259-66. doi: 10.1016/0167-4838(82)90359-4.
Different [7-3H]thymine preparations have been used to determine the inter- and intramolecular isotope effects of the 2-oxoglutarate-dependent thymine hydroxylation, catalyzed by thymine 7-hydroxylase (thymine, 2-oxoglutarate:oxygen oxidoreductase, EC 1.14.11.6). Specific activity ratios of products, viz., 3H2O and 5-hydroxymethyluracil, and remaining substrate to initial substrate have been determined. The influence on these ratios of intra- and intermolecular isotope effects at different degrees of tritium substitution has been analyzed. An intramolecular isotope effect with a kH/kT of about 6.5 has been found. No intermolecular isotope effect of TV/K could be detected when oxygen concentration was varied from 0.4 to 0.01 mM. This agrees with a mechanism in which 2-oxoglutarate is irreversibly changed before the bond-breaking in thymine takes place.
已使用不同的[7-³H]胸腺嘧啶制剂来确定由胸腺嘧啶7-羟化酶（胸腺嘧啶，2-氧代戊二酸：氧氧化还原酶，EC 1.14.11.6）催化的2-氧代戊二酸依赖性胸腺嘧啶羟基化反应的分子间和分子内同位素效应。已测定产物（即³H₂O和5-羟甲基尿嘧啶）以及剩余底物与初始底物的比活性。分析了不同氚取代程度下分子内和分子间同位素效应对这些比率的影响。发现分子内同位素效应的kH/kT约为6.5。当氧气浓度从0.4 mM变化到0.01 mM时，未检测到TV/K的分子间同位素效应。这与在胸腺嘧啶发生键断裂之前2-氧代戊二酸不可逆变化的机制相符。
