Concerted electron-proton transfer (EPT) in the oxidation of tryptophan with hydroxide as a base |
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Authors: | Gagliardi Christopher J Binstead Robert A Thorp H Holden Meyer Thomas J |
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Institution: | Department of Chemistry, University of North Carolina at Chapel Hill, North Carolina 27599-3290, USA. |
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Abstract: | Tryptophan is unique among the redox-active amino acids owing to its weakly acidic indolic proton (pK(a) ≈ 16) compared to the -O-H proton of tyrosine (pK(a) = 10.1) or the -S-H proton of cysteine (pK(a) = 8.2). Stopped-flow and electrochemical measurements have been used to explore the roles of proton-coupled electron transfer and concerted electron-proton transfer (EPT) in tryptophan oxidation. The results of these studies have revealed a role for OH(-) as a proton acceptor base in EPT oxidation of N-acetyl-tryptophan but not for other common bases. The reorganizational barrier for (N-acetyl-tryptophan)(+/?) self-exchange is also estimated. |
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