Long-range electron transfer in peptides. Tyrosine reduction of the indolyl radical: reaction mechanism, modulation of reaction rate, and physiological considerations

Abstract

We have observed long-range electron transfer (LRET) across the oligoproline spacer from the tyrosine side chain to the indolyl cation radical derived from the 1-electron oxidation of 1-N-methyltryptophan (Metrp .+ ). On the basis of these results and measured bimolecular electron transfers in the model system p-cresol/N-methylindole, phenol O-H bond breaking can clearly accompany the 1-electron transfer under conditions in which H-atom transfer to the indole nitrogen is impossible. With Metrp .+ as the electron acceptor, the rate of the LRET process across the oligoproline spacer is an order of magnitude higher than with the tryptophanyl radical (Trp . ) as electron acceptor