The replacement of 3'-OH of thymidine markedly influenced its catalytic activity with TP. The conversion of pyrimidine nucleosides with modified base moieties to the corresponding 1-phosphate form was poor. The leaving group activity decreased with an increase in aromaticity of the pyrimidine base moiety, because of increased difficulty in polarizing the base by the amino acids local to the active site
胸苷磷酸化酶(TP,
EC 2.4.2.4)通过碱基和
核糖基部分均以高特异性识别底物的结构。
胸苷的3'-OH取代显着影响TP的催化活性。具有修饰的碱基部分的
嘧啶核苷向相应的1-
磷酸酯形式的转化很差。离开基团的活性随着
嘧啶碱基部分的芳香性的增加而降低,这是因为增加了通过活性位点局部
氨基酸使碱基极化的难度。3'和5'官能团的替换趋于降低反应速率和TP转化率。特别地,
核糖基3'羟基在结构上对于酶与底物的结合是重要的。