Sodium Ions Affect the pH behavior of the Soluble Hydrogenase of Alcaligenes Eutrophus H16

Hydrogenase activity of the soluble hydrogenase from Alcaligenes eutrophus H16 was inhibited by monovalent cations in the order NaLiKNH4Cs. Hydrogenase activity was also slightly inhibited by monovalent anions. The Na -induced inhibition was not altered with varying NAD or H2 concentrations, suggesting that Na ions do not interfere with substrate binding. The inhibition was lowered when the H concentration was increased over a range of pH 8.5 to 7.0. Examination of the pH-velocity curve shows that NaC1 lowers and shifts the pH optimum in the acidic direction. These data suggest that Na ions bind to the enzyme, perhaps displacing protons.