ИСТИНА

The detection of biopolymers such as proteins and DNAs, is of a great significance for fundamental and applied biomedical studies as well as medical diagnostics. These macromolecules play crucial roles in biological processes, both in health and disease, and serve in many instances as disease markers. Electrochemical detection of proteins and DNAs through the direct redox reactions of their monomeric units, side chains of amino acid residues and nucleotides (direct electrochemistry) benefits from the simplicity, low cost, speed, and potential for miniaturization, thereby making it especially suitable for ‘point-of-care’ or ‘in-field’ testing. Moreover, direct electrochemistry allows one to detect biomolecular conformational changes, mutations, ligand binding, oxidative damage, and post-translational modifications [1-3]. At present, it is generally accepted that in proteins only Tyr, Trp, His, Met, Cys, and Cys-Cys residues can be electrochemically oxidized on solid (carbon) electrodes [2, 3], while in DNA molecules all nucleobases (G, A, T, and C) are known as electoactive [1, 4]. On carbon electrodes, the oxidation of protein and DNA molecules takes place at relatively high positive potentials (0.5 V and higher). The major drawback of direct biopolymer electrochemistry is a low level of registered currents. It is suggested that the specific electrocatalytic oxidation of amino acids and nucleobases may allow to overcome these problems. In this work, the electrochemical oxidation of protein and DNA molecules as well as their monomeric units (α, L-amino acids and nucleobases) was tested on bare and Prussian Blue (PB) modified carbon screen printed electrodes (SPE) by cyclic voltammetry and flow injection analysis. In contrast to the generally accepted point of view, the specific electrooxidation of nearly all proteinogenic amino acids, except for Glu, is revealed with constant potential (0.95 V) flow injection analysis on bare carbon SPEs. Furthermore, PB was found to catalyzed this electrooxidation. For 20 amino acids out of 21 tested, the electrogenerated Berlin Green (BG) has been reduced back to PB by amino acids, forming a catalytic cycle that resulted in an enhancement of oxidation signals. The most effective catalysis – the 54-, 31-, and 11-fold current enhancement – was observed for Gln, Ser, and His, respectively. The pronounced catalytic effect of electrogenerated BG on their oxidation has been observed for all proteins tested: human serum albumin, cytochrome c from equine heart, and equine skeletal muscle myoglobin. The same catalytic effect of PB was observed toward DNA from herring sperm, oligonucleotides, and nucleobases, while the electrochemical oxidation of guanosine and adenosine 5′-triphosphates has non been enhanced by PB. Presently, PB seems to be the only known material able to catalyze the specific electrochemical oxidation of nearly all protein and DNA molecules under physiological conditions (pH 6.0). Both the increased number of specifically oxidizable proteinogenic amino acids and the achieved efficient electrocatalysis of amino acids and nucleobases oxidation obviously opens new horizons for electrochemical detection of biopolymers (proteins, peptides, DNA, and oligonucleotides). This work was financially supported by the Russian Science Foundation, grant 19-14-00247. References: 1 V.C. Diculescu, A.M. Chiorcea-Paquim and A.M. Oliveira-Brett, Trends Analyt. Chem., 2016, 79, 23-36. 2 E.V. Suprun, V.V. Shumyantseva and A.I. Archakov, Electrochim. Acta, 2014, 140, 72-82. 3 E.V. Suprun, Trends Analyt. Chem., 2019, 116, 44-60. 4 J. Špaček, A. Daňhel, S. Hasoň and M. Fojta, Electrochem. Commun., 2017, 82, 34-38.