Lysine, Arginine, and Histidine Residues in Peptide‐Catalyzed Hydrogen Evolution at Mercury Electrodes

Abstract

Dedicated to Professor R. G. Compton on the Occasion of his 60 th Birthday 1IntroductionNucleic acids are electroactive species undergoing reduction and oxidation of their base residues at various types of electrodes.E lectrochemistry of nucleic acids embraces aw ide variety of natural and synthetic molecules including DNAand RNA [1][2][3].Incontrast, electrochemistry of proteins was concentrated mostly on the fast reversible electrode processes of non-protein redox centers in conjugated proteins [4][5][6][7][8].Recently,w eh ave shown that using constant-current chronopotentiometric stripping (CPS) in combination with mercury and amalgam electrodes,p ractically all proteins and many peptides produce the so-called peak H due to catalytic hydrogen evolution reaction (CHER,). Thep osition, height, shape,and area of this peak are sensitive to the analyte concentration and allow the detection of proteins in the nanomolar range. Application of CPS peak Hw as useful in the analysis of proteins such as determination of metalloproteins in tissues [12] and solubility of transmembrane proteins [13,14],m onitoring of protein aggregation [15,16] and denaturation [15,[17][18][19] [17,23].C PS peak Hi s ap owerful label-free electroanalytical signal useful in the contemporary protein research.To take full advantage of application of CPS peak Hi n the protein analysis,i ti se ssential to understand different parameters influencing the CHER. Modelp eptides [24,25] and polyamino acids [26,27] were used to explore the role of their amino acid (aa) composition [25] or interfacial organization of the adsorbed peptide layer on the CHER [28].I np eptides and proteins,o nly aa residues bearing functional groups with exchangeable protons should play the active role.W eh ave already shown that cysteine (Cys) thiol [20,24,28],l ysine (Lys) e-ammonium [27],a rginine (Arg) guanidinium or histidine (His) imidazolium groups [25] transfer the protons from the acid constituent of the buffer (proton donor) onto highly negatively charged surface of the electrode where they subsequently combine in more stable molecules of the gaseous hydrogen (H 2 ); for more details about the mechanism of the catalytic hydrogen evolution see e.g. [9].Thea bility of proteins to catalyze hydrogen evolution from aqueous solutions was discovered [29] soon after invention of polarography.T he so-called presodium wave on DC polarograms was too close to the background discharge and was considered of little analytical use.I tw as shown that the catalytic process is better developed in buffered media and application of polarography in studying the catalytic process was restricted to neutral or weakly alkaline media;a tp H < 7t his wave was masked by hydrogen evolution from the buffer [30].C ompared to DC polarography,c hronopotentiometry is highly sensitive to the catalysis of hydrogen evolution and CPS peak Hi s well separated from the background discharge even below pH 7[ 31].T his peak can be considered as as econd generation of the presodium wave [32,33].Recently,w e...

Chronopotentiometric Analysis of Proteins at Charged Electrode Surfaces

“…In the last decade, it has been found that amino acids (AA) containing labile protons such as cysteine, lysine, arginine, and histidine can be involved in CHER of peptides , polyamino acids and proteins themselves at neutral pH. Specifically, the proton‐exchangeable groups for individual AA are imidazolium (His), ϵ‐ammonium (Lys), guanidinium (Arg) and thiol group (Cys). His residues, at neutral pH, behaved as a weaker catalyst for CHER (considering pKa values) in comparison to Arg and Lys residues .…”

“…Specifically, the proton‐exchangeable groups for individual AA are imidazolium (His), ϵ‐ammonium (Lys), guanidinium (Arg) and thiol group (Cys). His residues, at neutral pH, behaved as a weaker catalyst for CHER (considering pKa values) in comparison to Arg and Lys residues . Cys participation in CHER was studied in earlier works dealing with the peak H .…”

“…In this case, the first peak appears from the AA residues that are in direct contact with the electrode surface and the second, more negative peak from the residues that are located farther from the electrode surface. Another explanation of this phenomenon could be associated with the fact that some proton‐exchangeable AA groups can yield protons easier (at less negative potentials) as other AA groups .…”

Chronopotentiometry as a Sensitive Interfacial Characterisation Tool for Peptide Aptamer Monolayers

“…In light of this accumulated knowledge it is not surprising that the Cys‐p53 aptamer exhibits a good catalytic activity towards the hydrogen evolution at the mercury electrode. Indeed, around the physiological pH, the amino acid residues which are the most active for the catalytic hydrogen evolution reaction are Cys, Lys, and Arg , the aptamer containing the former two. In addition, the peptide must be present at the electrode at the potential (and at the moment) at which the catalysis takes place.…”

BSA‐Polysaccharide Interactions at Negatively Charged Electrode Surface. Effects of Current Density.

“…This method represents a rapid analysis of the nanomolar concentrations of particularly all proteins without any additional labelling or modification . The CPS signal of a protein was denominated as “peak H” and its appearing in the protein analysis is a result of catalytic hydrogen evolution reaction (CHER) of amino acids residues bearing exchangeable proton, such as Cys, Arg, Lys, and His . Global and local changes in the protein structure such as denaturation , mutation , chemical modification , damage , redox state , and aggregation can be studied using CPS due to susceptibility of proteins to effects of electric field.…”