Protein phosphorylation by kinases plays a significant role in a wide range of cellular processes. Phosphotyrosine is the product of tyrosine phosphorylation. The electrochemical behaviour of phosphotyrosine (pTyr) at a glassy carbon electrode was investigated over a wide pH range, using cyclic, differential pulse and square-wave voltammetry. The oxidation is an irreversible, pH-independent process that involves the transfer of one electron and no proton. The oxidation of phosphotyrosine occurs in a cascade mechanism and for acid electrolytes one electroactive product was observed. In neutral and alkaline electrolytes two redox products that undergo reversible, pH-dependent redox reactions with the transfer of two electrons and two protons were characterised. Also, the oxidation of tyrosine was studied in order to find information about the redox products of phosphotyrosine. A redox mechanism for phosphotyrosine was proposed. The present study provides information concerning an electroanalytical signal for studying protein phosphorylation processes. (C) 2012 Elsevier B.V. All rights reserved.