AbstractPhotochemical mapping of nucleophiles in close proximity to the active site Cys149 of rabbit glyceraldehyde‐3‐phosphate dehydrogenase (GAPDH) was demonstrated based on the nucleophilic aromatic photosubstitution reaction using two regioisomers of alkoxy‐fluoro‐nitro‐substituted benzenes. Two photophores were covalently attached to the active site SH group of GAPDH and the protein was subjected to photolysis then to the cyanogen bromide cleavage reaction. The advantage of this method is the capability to chase labeled products by monitoring absorption at 380 nm because of the chromogenic property of photophore. HPLC separation identified a large labeled peptide fragment that was further digested by V8 protease for Edman sequence analysis. From the recent X‐ray crystallography of rabbit GAPDH, Tyr311, His176, Ser238 and Lys183 are closely located to catalytic Cys149. Among these nucleophiles, Tyr311 was preferentially labeled with 2‐fluoro‐4‐nitrophenoxy photophore and no label was identified with the isomeric 4‐fluoro‐2‐nitrophenoxy photophore. The result clearly reflects the distance between Cys149 and nucleophiles to distinguish the nearest Tyr311. As photophores show great reactivity even with water under neutral conditions, the distance between nucleophiles and photophores is important for photo‐induced nucleophilic aromatic substitution. The method will provide a useful technique to survey nucleophiles within the catalytic domain.
摘要利用烷氧基-氟-硝基取代苯的两个区域异构体进行亲核芳香族光取代反应,证明了靠近兔甘油醛-3-磷酸脱氢酶(GAPDH)活性位点 Cys149 的亲核物的光化学图谱。两个光敏剂共价连接到 GAPDH 的活性位点 SH 基团上,然后对蛋白质进行光解,再进行溴化氰裂解反应。这种方法的优点是,由于光团具有发色性,可以通过监测 380 纳米波长的吸收来追寻标记产物。高效液相色谱分离确定了一个大的标记肽片段,该片段被 V8 蛋白酶进一步消化,用于 Edman 序列分析。根据最近对兔 GAPDH 的 X 射线晶体学研究,Tyr311、His176、Ser238 和 Lys183 与催化 Cys149 的位置非常接近。在这些亲核物中,Tyr311 优先被 2-氟-4-硝基苯氧基光致发光体标记,而同分异构的 4-氟-2-硝基苯氧基光致发光体则没有标记。这一结果清楚地反映了 Cys149 与亲核物之间的距离,以区分最近的 Tyr311。由于在中性条件下,亲光体甚至与水也有很大的反应活性,因此亲核物与亲光体之间的距离对于光诱导的亲核芳香取代非常重要。该方法将为研究催化域内的亲核物提供有用的技术。