COMPARISON OF THE ADSORPTIVE VOLTAMMETRIC BEHAVIOR OF AVIDIN AND STREPTAVIDIN

The adsorptive voltammetric behavior of the binding proteins avidin and streptavidin was investigated at a stationary mercury drop electrode. It is demonstrated that, although streptavidin contains no disulfide linkages or sulfur-containing amino acids, it gives rise to voltammetric behavior similar to avidin, which is a glycoprotein containing two cysteine residues per subunit and one interchain disulfide linkage. The adsorptive accumulation of both proteins was investigated both at open circuit and under electrolytic conditions. It is shown that avidin shows preferential adsorption characteristics under open circuit conditions, and under electrolytic conditions when the potential of the electrode was held at positive potentials. Streptavidin, on the other hand, shows preferential adsorption characteristics when accumulation is carried out at open circuit. This behavior is explained by considering the charged nature of the proteins under the experimental conditions used in this study. It would appear, therefore, that the voltammetric peaks obtained for globular and other proteins not containing prosthetic groups are due in part to processes other than the simple reduction of the disulfide linkage.