Oxidoreductases use metallocofactors, organic molecules, and four amino acids (Tyr, Trp, Cys, and Gly) to perform electron transfer (ET) and proton-coupled electron transfer (PCET) reactions. These four amino acids serve as one-electron (radical) redox mediators in biocatalytic and multistep electron/hole transfer processes, some of which are essential to life on earth. There is also a sinister side to amino-acid ET/PCET since these reactions can be induced at oxidative stress conditions and cause significant cellular damage. It is extremely challenging to experimentally resolve the thermodynamic and kinetic redox properties of a single amino-acid residue. Consequently, key information to support the understanding of one of nature's essential redox tools is missing. Our research focuses on developing a family of well-structured model proteins with the unique capability of providing detailed mechanistic information on Tyr (Y) and Trp (W) oxidation-reduction reactions.