Reduction of transient histidine radicals by tryptophan: influence of the amino group charge

Second-order rate constants of the reduction of histidine radicals by tryptophan were obtained for all combinations of the two amino acids and their N-acetyl derivatives. For the dipeptide N-acetyl histidine-tryptophan, contributions from inter- and intramolecular reduction were revealed. The pH dependences of the rate constants were found to be determined by the protonation state of the amino group of tryptophan. Proton coupled electron transfer is proposed as a reaction mechanism.

Automated summary

The second-order rate constants of histidine radicals reduced by tryptophan were obtained for different combinations of amino acids and their N-acetyl derivatives. Contributions from inter- and intramolecular reduction were revealed for the dipeptide N-acetyl histidine-tryptophan. The pH dependences of the rate constants were determined by the protonation state of tryptophan's amino group, suggesting a possible reaction mechanism of proton coupled electron transfer.