Redox (In)activations of Metalloenzymes: A Protein Film Voltammetry Approach

Abstract

Redox metalloenzymes are omnipresent in living organisms where they catalyze key cellular reactions with great efficiency. These enzymes can often be reversibly placed into inactive states following changes in redox conditions. This is a hindrance for their use in biotechnological devices, and also a complication for their study via a structure/function approach, because structural data alone usually is not enough to discriminate between active and inactive states. However, these inactive states can also inform on the chemistry of the enzyme's active sites and on their catalytic cycles. A technique that has proved particularly valuable in the last decades for studying these processes is protein film voltammetry (PFV), in which an enzyme is immobilized on an electrode in a configuration where direct electron transfer is possible. In this article, we review the studies of redox (in)activation processes using PFV, present the theory for a number of cases (reversible inactivations, irreversible activations), and give guidelines to obtain and interpret suitable kinetic data.[a] Dr. M. del Barrio, Dr. V. Fourmond

A safety cap protects hydrogenase from oxygen attack

“…We examined the kinetics and potential-dependence of anaerobic (in)activation, which can be quantitatively probed using PFE by potential-step experiments 40 . Figure 4 a shows a typical sequence of steps and the resulting change in current.…”

Reversible catalysis

“…In the case of non precious metals and metal alloys, surface oxidation occurs under OER conditions, with the formation of surface oxides and hydroxides that are not present under the reductive conditions required for the ORR 30,31 . Regarding metalloenzymes, a slow redox-driven structural modification of the active site can also result in a loss of activity under very oxidizing or reducing conditions 32 . This is common for This is a post-peer-review, pre-copyedit version of an article in press.…”

Mechanism of Hydrogen Sulfide-Dependent Inhibition of FeFe Hydrogenase

“…The kinetics of redox-dependent (in)activation is more easily investigated in chronoamperometry (CA) experiments than in cyclic voltammetry. 41 Figure 3A shows a typical CA experiment in the presence of HS -/H 2 S, in which the H 2 oxidation current was monitored over time during a sequence of potential steps. After each potential step up or down, the current instantaneously changes as a result of the dependence on potential of the steady-state turnover frequency of the enzyme, and then slowly changes as a result of inactivation or reactivation ; that H 2 S slowly leaves the cell results in the the observed very slow reactivations at E = 10mV.…”