Electrochemical Consideration of Electrostatic Interaction of Charged Molecules with Partially Overlapped Electric Field: Zwitterions and Proteins

Abstract

Electrostatic interactions greatly affect the interaction and activity of ions and charged molecules. In this study, electrochemical techniques were applied to evaluate the electrostatic interactions of zwitterions and proteins as charged molecules that have partially overlapped electric field. The formal potential of a probe redox couple, [Fe(CN)6]3−/4−, was used as a measure of the electrostatic interaction between the probe ions and linear amino acids as zwitterions. The zwitterions clearly showed electrostatic interaction with [Fe(CN)6]3−/4−, but the strength was weakened by the partial overlapping of the electric field of oppositely charged sites. Furthermore, we investigated the electrostatic interaction between proteins as multivalent polymeric ions using quinohemoprotein amine dehydrogenase and its electron accepter proteins (amicyanin, cytochrome c550, and horse heart cytochrome c). The second-order reaction rate constant (k) of the intermolecular electron transfer between the proteins was electrochemically determined in various ionic strengths (I). The I dependences of k were explained not by the net charges but by the local charges around the interaction interfaces of the proteins.

Keywords

• electrostatic interaction
• zwitterion
• quinohemoprotein amine dehydrogenase
• local charge