Correction for Hexter et al., Electrocatalytic mechanism of reversible hydrogen cycling by enzymes and distinctions between the major classes of hydrogenases

CHEMISTRY Correction for “Electrocatalytic mechanism of reversible hydrogen cycling by enzymes and distinctions between the major classes of hydrogenases,” by Suzannah V. Hexter, Felix Grey, Thomas Happe, Victor Climent, and Fraser A. Armstrong, which appeared in issue 29, July 17, 2012, of Proc Natl Acad Sci USA (109:11516–11521; first published July 16, 2012; 10.1073/pnas.1204770109).

The authors note that on page 11517, right column, fourth full paragraph, lines 4–5, “k_min = k⁰ and k_max = k⁰exp(−βd₀)” should instead appear as “k_max = k⁰ and k_min = k⁰exp(−βd₀).”

Also, on page 11518, left column, fourth full paragraph, line 8, “e₂ = k_2a/k_2c” should instead appear as “e₂ = k_2c/k_2a.”

Figs. 4, 5, and 6 and the legend for Figure 5 appeared incorrectly. The corrected figures and their legends appear below.

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).

Fig. 5.

Cyclic voltammograms (symbols) obtained for four hydrogenases as indicated in each panel and the corresponding fits to Eq. 8 (lines). Experimental conditions: pH 6.0 standardized at 30 °C, ω = 2500 rpm, ν = 5 mV s⁻¹, 100% H₂; numbers by each voltammogram refer to temperature in degrees Celsius. Simulation parameters considered not to vary with temperature are as follows: CaHydA, E⁰_Ox/R = −0.40 V, βd₀ = 4.2; CrHydA1, E⁰_Ox/R = −0.36 V, βd₀ = 5.1; EcHyd2, E⁰_Ox/R = −0.30 V, βd₀ = 12.0; EcHyd1, E⁰_Ox/R = −0.19 V, βd₀ = 11.0.

Fig. 6.

(A and B) Parameters corresponding to the best fits of Fig. 5, for experiments at 22 °C, except CrHydA1 where data obtained at 18 ºC. (C and D) Activation enthalpies at E⁰_Ox/R from the temperature variation of j_lim and k⁰, giving the activation energy for the chemical step in the anodic direction, , and the activation energy for the electron transfer step, , respectively.