Oxidation of tryptophan and N-methylindole by N3.cntdot., Br2.-, and (SCN)2.- radicals in light- and heavy-water solutions: a pulse radiolysis study
摘要:
Reactions of N3., Br2.-, and (SCN)2.- with tryptophan (TRPH) and N-methylindole (NMI) have been investigated in H2O and D2O solutions. The main transients produced were the TRP. radical and the TRPH.+ radical cation from TRPH and the NMI.+ radical cation from NMI. Their extinction coefficients (epsilon) as well as the rate constants for their formation and decay were determined in the pH range 3-10. The pK of the TRPH.+ radical cation was confirmed to be 4.2 +/- 0.1. These rate constants were within experimental error, independent of pH, and the differences between the rate constants in H2O and D2O were small. On the basis of the results, it was concluded that of the two possible reactions-electron or hydrogen atom transfer-the data are more consistent with electron transfer in all cases. However, secondary acid-base reactions have an important effect on the overall redox equilibria, especially with N3.. Experimental data on these effects have also been obtained.
Reversibility of charge transfer between tryptophan and tyrosine
作者:John Butler、Edward J. Land、Walter A. Prütz、A. John Swallow
DOI:10.1039/c39860000348
日期:——
Whereas tryptophan radicals oxidise tyrosine over a wide range of pH values, the one-electron reduction potential of the electron-deficient tryptophan radical at pH 7 is only 0.093 V more positive than that of the corresponding tyrosine radical, so that the reaction proceeds in reverse in strongly acid and alkaline solution.