Oscillating hydrogenase reaction

• If no pH is adjusted, H2 oxidation reaction of hydrogenase presents oscillations.
• Oscillation is due to the presence of autocatalytic step in hydrogenase reactions.
• pH shift of H2 oxidation and proton reduction reactions causes the oscillation.

The hydrogenase-catalyzed oxidation of H2 includes an autocatalytic step in the reaction cycle. The reaction also exhibits different pH dependence in the H2 oxidation and in the proton reduction directions. This is not only due to the pH titration of the amino acid side chains as protons are also either the substrates or the products of the reaction. Utilizing the autocatalytic nature of the hydrogenase reaction and the multiple roles of protons therein, together with appropriate limitation of the substrate (gaseous H2) supply, oscillations can be induced in the system. The reaction oscillates both in space and in time, and can last for days with decreasing frequency until reaching chemical equilibrium. Of all biological oscillating systems described so far, this one is the simplest in that it has the fewest biological components.