The relationship between redox enzyme activity and electrochemical potential—cellular and mechanistic implications from protein film electrochemistry

Abstract

In protein film electrochemistry a redox protein of interest is studied as an electroactive film adsorbed on an electrode surface. For redox enzymes this configuration allows quantification of the relationship between catalytic activity and electrochemical potential. Considered as a function of enzyme environment, i.e., pH, substrate concentration etc., the activity-potential relationship provides a fingerprint of activity unique to a given enzyme. Here we consider the nature of the activity-potential relationship in terms of both its cellular impact and its origin in the structure and catalytic mechanism of the enzyme. We propose that the activity-potential relationship of a redox enzyme is tuned to facilitate cellular function and highlight opportunities to test this hypothesis through computational, structural, biochemical and cellular studies.

Explorations of time and electrochemical potential: opportunities for fresh perspectives on signalling proteins

“…Direct chemical insight into the nature of a redox cofactor is not afforded by cyclic voltammetry. However, this disadvantage is outweighed by the quantitative insights into thermodynamic and kinetic properties of the protein that are afforded by virtue of having the entire sample under precise potential control at all times in the experiment [10,11].…”

“…Protein film electrochemistry has the advantage of requiring minuscule amounts of protein, typically less than 1 pmol when using graphite or modified gold electrodes. It has been applied successfully to many redox-active proteins containing transition metals and flavins (for examples, see [10,11]). It can also characterize cysteine/disulfide redox transitions [18].…”

“…Protein film electrochemistry provides an alternative to spectroelectrochemistry for resolving protein redox activity (see [10,11] and references therein). Here, the sample is adsorbed on an electrode surface as a film of up to monolayer coverage in which it displays properties relevant to its behaviour in its cellular context.…”

“…The protein's response to this stimulus is then assessed as a spectroscopic signal and/or a flow of electrical current that reports on thermodynamic, kinetic and chemical aspects of the protein's redox chemistry. These properties have resulted in widespread use of electrochemical methods in studies of respiratory and photosynthetic proteins (see [10,11] and references therein). The present article illustrates how electrochemical methods can assist in the characterization redox signalling by considering two studies, namely spectroelectrochemical characterization of the cardiolipin complex of cytochrome c and protein film electrochemistry of glutaredoxin 2.…”

Electrochemical titrations and reaction time courses monitored in situ by magnetic circular dichroism spectroscopy

“…Thus, the introduction of substrate into a stirred solution contacting an adsorbed electroactive protein film offers the prospect of resolving the oxidation, ligation, and spin states of the predominant enzyme form(s) present during steady-state catalysis at defined electrochemical potential. Such experiments are likely to provide valuable insight into the variation of catalytic rate-defining events with applied potential, an area where much remains to be elucidated [50]. …”