Radical Formation and Migration in Myoglobins

• Published in: Progress in Reaction Kinetics and Mechanism
• Main Authors: Svistunenko, Dimitri A., Reeder, Brandon J., Wilson, Michael T., Cooper, Chris E.
• Format: Article in Journal/Newspaper
• Language: English
• Published: SAGE Publications 2003
• Subjects: Sperm whale
• Online Access: http://dx.doi.org/10.3184/007967403103165477; https://journals.sagepub.com/doi/pdf/10.3184/007967403103165477

Three EPR signals from individual free radical species have been identified in the EPR spectra of horse heart metmyoglobin (HH metMb) mixed with hydrogen peroxide (H 2 O 2 ). The peroxyl radical EPR signal was assigned to the Trp14-OO • radical, the seven component signal – to the Tyr103 • radical and the singlet EPR signal was assigned to the Tyr146 • radical. Apo-Mb (haem free HH Mb) added in various concentrations to the native metMb prior to H 2 O 2 addition affected the yields of the three types of radicals. As the concentrations of metMb and H 2 O 2 were kept constant, the yield of the primary radical formed is the same in all experiments, H 2 O 2 being unable to produce any radical in the reaction with a haem free protein. Nevertheless, the addition of apo-Mb resulted in an increase of the Tyr146 • radical concentration and in a quantitatively similar decrease of the Tyr103 • radical concentration. These changes were dependent on the concentration of the added apo-Mb. Thus we show that a radical transfer Tyr103 • → Tyr146 • occurs and that this reaction is protein concentration dependent. The question whether this radical transfer is inter- or intra-molecular is discussed. A similarity is drawn between the system studied and the sperm whale metMb/H 2 O 2 system, for which the radical transfer Tyr103 • → Tyr151 • has been previously suggested.