2,3-Difluorotyrosine at Position 356 of Ribonucleotide Reductase R2: A Probe of Long-Range Proton-Coupled Electron Transfer

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• 作者：Cyril S. Yee ; Michelle C.Y. Chang ; Jie Ge ; Daniel G. Nocera ; and JoAnne Stubbe
• 刊名：Journal of the American Chemical Society
• 出版年：2003
• 出版时间：September 3, 2003
• 年：2003
• 卷：125
• 期：35
• 页码：10506 - 10507
• 全文大小：110K
• 年卷期：v.125,no.35(September 3, 2003)
• ISSN：1520-5126

文摘

Escherichia coli class I ribonucleotide reductase catalyzes the conversion of ribonucleotides to deoxyribonucleotides and consists of two subunits: R1 and R2. R1 possesses the active site, while R2 harbors the essential diferric-tyrosyl radical (Ys/entities/bull.gif">) cofactor. The Ys/entities/bull.gif"> on R2 is proposed to generate a transient thiyl radical on R1, 35 Å distant, through amino acid radical intermediates. To study the putative long-range proton-coupled electron transfer (PCET), R2 (375 residues) was prepared semisynthetically using intein technology. Y356, a putative intermediate in the pathway, was replaced with 2,3-difluorotyrosine (F₂Y, pK_a = 7.8). pH rate profiles (pH 6.5-9.0) of wild-type and F₂Y-R2 were very similar. Thus, a proton can be lost from the putative PCET pathway without affecting nucleotide reduction. The current model involving Hs/entities/bull.gif"> transfer is thus unlikely.