Fig. 3.

Inactivation of CrHydA1 by O₂ as compared to inhibition by CO, and protection by CO against O₂ inactivation. (A) Inactivation and inhibition by 10% O₂ (i, red trace) and 10% CO (ii, blue trace) by gas exchange. The black trace shows an experiment in which the enzyme was subjected to 10% O₂ after being fully inhibited by 10% CO (iii). The dotted line gives a visual guide to the progression of background film loss. Experimental conditions: pH 6.0, 20 °C, electrode rotation rate 3,000 rpm, −0.05 V vs. SHE, gas mixtures in the headspace as indicated, with 80% H₂ and balance of N₂ making up the remainder of the headspace atmosphere. The timeline shown in the lower panel provides a guide for the sequence of gas changes. (B) Dependence of rate of inactivation on concentration of O₂ (diamonds, red) and CO (squares, blue). Note the rates of inactivation by CO were calculated by performing experiments such as those shown in Fig. 2, that is, by simultaneous injection of CO-saturated buffer and gas exchange.