FIG. 5.

Effect of acetylene on the H-D exchange reaction catalyzed by the hupSL-encoded hydrogenase (A) and by the hupUV-encoded hydrogenase (B). The conditions were the same as those in Fig. 4, with cells grown overnight anaerobically in the light in MN medium. H₂ (▄ ▄ ▄) and HD (····) production in exchange with D₂ (––––) uptake catalyzed by whole cells of BSE16 (2.5 mg of protein) (A) and JP91(pAC206) (5.2 mg of protein) (B) was measured at pH 7 after the cells had been incubated for 1 h at room temperature under a gas phase of C₂H₂-Ar (1:1). The figure shows the real concentrations of the hydrogen species in the vessel.