Fig. 4.

The apparent activation enthalpies across a range of ca. 0.8 V for four different hydrogenases, as indicated in the figure. The data were obtained from the Eyring plots of the voltammetric currents recorded over a range of temperatures. The error bars reflect the variations in the slopes of Eyring plots obtained from experiments carried out with different enzyme films. Data from potentials at which oxidative inactivation processes occur have not been included. The shaded area depicts the range of ΔH^‡ values reported for the exchange current at Pt (32).