Pincus M R, Hummel C F, Brandt-Rauf P W, Carty R P
Department of Biochemistry, State University of New York, Brooklyn.
Int J Pept Protein Res. 1990 Jul;36(1):56-66. doi: 10.1111/j.1399-3011.1990.tb00083.x.
The binding and alkylation rate constants for the reaction of four bromoacetamido pyrimidine nucleosides and bromoacetamide with bovine pancreatic ribonuclease A (RNase A) have been determined as a function of temperature. The four nucleoside derivatives react exclusively or preferentially with the NE2 atom of histidine-12 and include 2'-bromoacetamido-2'-deoxyuridine, 2'-bromoacetamido-2'deoxyxylofuranosyluracil, 3'-bromoacetamido-3'-deoxythymidine and 3'-bromoacetamido-3'-deoxyarabinofuranosyluracil. Transition-state parameters, delta H++ and delta S++, reveal that nucleosides with "up" OH groups experience relative rate enhancements which have been attributed to contacts between these groups and the enzyme in the transition state (1). Variations in alkylation rates are explained in terms of different degrees of entropic destabilization (2) of the nucleosides in the enzyme.affinity label complex.
已测定四种溴代乙酰氨基嘧啶核苷和溴乙酰胺与牛胰核糖核酸酶A（RNase A）反应的结合速率常数和烷基化速率常数随温度的变化情况。这四种核苷衍生物仅与或优先与组氨酸-12的NE2原子反应，包括2'-溴代乙酰氨基-2'-脱氧尿苷、2'-溴代乙酰氨基-2'-脱氧木糖呋喃糖基尿嘧啶、3'-溴代乙酰氨基-3'-脱氧胸苷和3'-溴代乙酰氨基-3'-脱氧阿拉伯呋喃糖基尿嘧啶。过渡态参数ΔH++和ΔS++表明，具有“向上”羟基的核苷经历了相对速率增强，这归因于这些基团与过渡态酶之间的接触（1）。烷基化速率的变化根据核苷在酶-亲和标记复合物中的不同程度的熵不稳定来解释（2）。
