Electrochemical study of ricin at glassy carbon electrode

• Published in: Analyst (London) 2013-08, Vol.138 (16), p.4565-4573
• Main Authors: Ribeiro, Williame F, da Costa, Daniel J. E, Loureno, Anabel S, Lopes, Ilanna C, de Medeiros, Everaldo P, Salazar-Banda, Giancarlo R, do Nascimento, Valberes B, de Arajo, Mrio C. U
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Carbon - chemistry; Cysteine; Electrochemical Techniques - methods; Electrodes; Glass - chemistry; Glassy carbon; Mathematical analysis; Molecular Sequence Data; Oxidation; Polypeptides; Protein Structure, Secondary; Ricin - analysis; Ricin - genetics; Voltammetry
• ISSN: 0003-2654; 1364-5528
• DOI: 10.1039/c3an00227f

Ricin, Ricinus communis agglutinin 60 RCA 60, is a deadly phytotoxic protein which inhibits ribosomes (class II), and there is no known effective antidote in living organisms. Ricin is composed of two polypeptide chains, A and B, linked covalently by a single disulfide bond. The analytical methods for the detection of RCA 60 are commonly laborious, expensive, require skilled labor, and involve sophisticated equipment. Aimed at the development of electroanalytical methods for RCA 60 detection, here we studied the electrochemical oxidation of RCA 60 on a glassy carbon (GC) electrode over a wide pH range, using cyclic voltammetry, differential pulse voltammetry (DPV) and square wave voltammetry (SWV). Two quasi-reversible electrochemical RCA 60 oxidation peaks were identified on the GC electrode by SWV. For values of 2.2 pH 10.2, DPV studies revealed that the peak potentials, E P 1 and E P 2 , display a linear dependence with pH and the reaction mechanism involves the transfer of 2H + /2e (peak 1) and 1H + /1e (peak 2). The first and second RCA 60 oxidation steps may correspond to the oxidation of cysteine and tyrosinetryptophan residues, respectively. The oxidation product of the second RCA 60 oxidation step appears at 7.0 pH 11.8. For pH 10.2, both processes are pH independent, resulting in a p K a of ca. 10.2. A third RCA 60 oxidation peak only appears at acidic pH. RCA 60 samples extracted from different castor seed cultivars showed similar electrochemical behavior, enabling the implementation of an analytical voltammetric method. The electrochemical oxidation of RCA 60 at a GC electrode is quasi-reversible and pH-dependent. The first and second RCA 60 oxidation steps may correspond to the oxidation of cysteine and tyrosinetryptophan residues, respectively.