Electroactivity of Avidin and Streptavidin. Avidin Signals at Mercury and Carbon Electrodes Respond to Biotin Binding

Abstract

Avidin and streptavidin were studied by phase-sensitive AC and cyclic voltammetry as well as by constant current chronopotentiometry at mercury (in alkaline media) and carbon electrodes (in acid medium). In contrast to the generally accepted belief that these proteins are electroinactive, we observed various electrochemical responses at these electrodes. Both proteins produced peaks due to oxidation of tyrosine and tryptophan residues at carbon electrodes and a catalytic peak H at a hanging mercury drop electrode. At the latter electrode avidin produced phasein AC voltammetric and cyclic voltammetric peaks close to À 0.6 V (peak S) which were assigned to Hg-S interactions, involving cystine/cysteine residues. In cobalt containing solution avidin produced a characteristic catalytic double wave requiring presence of cystine/cysteine residues in the protein molecule. Streptavidin, which does not contain these residues, yielded neither the catalytic double wave nor peak S. All the above avidin signals responded to biotin binding; peak S increased (up to 4 biotin molecules bound) while other avidin signals decreased as a result of biotin binding. A tentative scheme of interfacial behavior of avidin and avidin-biotin complex, depending on the electrode charge, was suggested.

Electroactivity of Nonconjugated Proteins and Peptides. Towards Electroanalysis of All Proteins

“…1D and 2) and B) at mercury electrodes i) cysteine (Cys) residues can form compounds with the electrode mercury at positive potentials and the HgS bond can be reduced (Fig. 1B) at negative potentials [18,67,73]. ii) Reduction of disulfide groups in some proteins were reported [3, 74 -77].…”

Chronopotentiometric Determination of Redox States of Peptides

“…In the presence of both the reduction and denaturing agents (urea or guanidine) this increase was larger. CPS peak H probably reflects similar electrode processes as the so-called DC polarographic pre-sodium wave [17,32] but this peak is better developed, allowing determination of nanomolar and subnanomolar concentrations of peptides and proteins [23,25,28,29]. Several factors contribute to the better sensitivity of the CPS peak H as compared to DC polarography: (i) In CPSA more negative potentials can be reached [43,44] than in voltammetry and polarography.…”

Streptavidin Modified Carbon Nanotube Based Graphite Electrode for Label‐Free Sequence Specific DNA Detection

“…Under this scope, a series of experiments were performed using concentration levels for STR and bio-ODN of 2000 mg mL À1 and 100 mg mL À1 , respectively. In the case of STR modified CNT-PGEs, the voltammogram showed a broad peak at potential of þ 0.798 V (shown in Figure 1Ab), which is attributed to tryptophan and tyrosine residues in STR that can be oxidized electrochemically at carbon electrodes [29,30]. The biotinylated DNA attachment onto STR coated surface caused a decrease at the signal of STR ( Figure 1Ac) as a result of the specific and strong binding between STR and biotin.…”

“…Covalent activation was performed as reported by Millan et al [30] by using EDC and NHS solutions in PBS. 1 mg of functionalized MWNTs were dispersed in 1 mL of EDC/ NHS solution and the resulting solution (1 : 1) was sonicated for 45 minutes in order to activate the carboxylic acid groups of the CNTs through the formation of an NHS ester intermediate.…”