Department of Chemistry, University of North Carolina at Chapel Hill, North Carolina 27599-3290, USA.
J Am Chem Soc. 2011 Dec 14;133(49):19594-7. doi: 10.1021/ja207379n. Epub 2011 Nov 16.
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.
色氨酸由于其弱酸性吲哚质子（pK(a) ≈ 16）与酪氨酸的-O-H 质子（pK(a) = 10.1）或半胱氨酸的-S-H 质子（pK(a) = 8.2）相比，在氧化还原活性氨基酸中是独特的。停流和电化学测量已被用于探索质子偶联电子转移和协同电子质子转移（EPT）在色氨酸氧化中的作用。这些研究的结果表明，OH(-)作为 EPT 氧化 N-乙酰色氨酸的质子接受碱的作用，但不是其他常见碱的作用。（N-乙酰色氨酸）+/•自交换的重组障碍也被估算。
