First-principles study of muon and muonium trapping in the protein chain of cytochrome c

For the interpretation of data on electron transfer in proteins from muon spin relaxation (μSR) measurements, we have already theoretically investigated the trapping of the positive muon (μ⁺) and muonium (Mu) in a number of single amino acids occurring in cytochrome c. We are now focusing on a sequence of amino acid molecules in cytochrome c that constitutes about 25% of the total protein chain, to test the attractiveness of different groups for μ⁺ and Mu. Both the differences in properties between individual amino acids and a particular amino acid in different parts of the protein chain provide detailed insights into environmental effects and the nature of the differences between different amino acids in the protein chain. The importance of these features for the interpretation of μSR data is discussed.