Mechanistic Insight into Tyrosine Oxidation Revealed by Fast-Scan Cyclic Voltammetry

Tyrosine (Tyr) is an electroactive amino acid with diverse functions in biological systems. A comprehensive understanding of its redox behavior is essential, as it can allow for accurate in vivo monitoring and shed light on complex biochemical processes. However, the study of Tyr using voltammetric techniques is hindered by electrode fouling, complicating data interpretation. In this study, fast-scan cyclic voltammetry (FSCV) was used for accurate and reproducible analysis of Tyr redox properties, before significant accumulation of byproduct on the carbon-fiber microelectrode surface. At a scan rate of 100 V/s, Tyr exhibited a distinct peak indicative of irreversible voltammetry and consistent with theoretical models combining both surface-adsorbed and diffusing Tyr species. FSCV was further utilized to study the adsorption properties and proton-coupled electron transfer (PCET) of Tyr when incorporated into various small peptides. The results showed that variations in oxidation potential and electron transfer rates were influenced by Tyr's position relative to the C- or N-terminus and the hydrophobicity of nearby amino acids. Additionally, FSCV was demonstrated to be an effective technique for studying electrochemical-chemical (EC) reaction mechanisms associated with Tyr oxidation. Scans conducted up to 1.4 V (vs Ag/AgCl) resulted in the formation of byproducts on the electrode surface with voltammetric properties similar to DOPA. A different byproduct was observed when the switching potential was limited to lower values, indicating complexity in the EC mechanism. Overall, these studies mark the first application of FSCV to characterize Tyr redox chemistry at carbon-fiber microelectrodes. The findings are important for developing effective anti-fouling strategies and enabling detailed exploration of Tyr and Tyr-containing neurotransmitters in biological systems.