FIG. 4.

Time course of H₂ and HD production and D₂ consumption in the D₂-H₂O system by the HupSL (A) and HupUV (B) protein complexes. Cells were grown anaerobically in the light in MN medium. The H-D exchange reaction in whole cells of BSE16, a ΔhupUV mutant (2.5 mg of protein) (A), and in whole cells of JP91(pAC206), a hupSL mutant, with the hupTUV operon-containing plasmid pAC206 (5.2 mg of protein) (B), was measured in 50 mM citrate-phosphate buffer (pH 7.0). At the time indicated by the vertical dotted line, the reaction vessel was closed, and the concentrations of D₂ (▄), H₂ (----), and HD (····) were recorded. The arrows indicate the time of O₂ appearance in the medium after H₂O₂ addition (2 μl of 0.3% H₂O₂) and the time of ferricyanide addition (10 mM). The changes in O₂ concentration were monitored at a mass of 32 Da (data not shown). The figure shows the real concentrations of the hydrogen species present in the vessel.