Nickel-Substituted Rubredoxin as a Minimal Enzyme Model for Hydrogenase.

A simple, functional mimic of [NiFe] hydrogenases based on a nickel-substituted rubredoxin (NiRd) protein is reported. NiRd is capable of light-initiated and solution-phase hydrogen production and demonstrates high electrocatalytic activity using protein film voltammetry. The catalytic voltammograms are modeled using analytical expressions developed for hydrogenase enzymes, revealing maximum turnover frequencies of approximately 20-100 s(-1) at 4 °C with an overpotential of 540 mV. These rates are directly comparable to those observed for [NiFe] hydrogenases under similar conditions. Like the native enzymes, the proton reduction activity of NiRd is strongly inhibited by carbon monoxide. This engineered rubredoxin-based enzyme is chemically and thermally robust, easily accessible, and highly tunable. These results have implications for understanding the enzymatic mechanisms of native hydrogenases, and, using NiRd as a scaffold, it will be possible to optimize this catalyst for application in sustainable fuel generation.