Fixation of molecular tritium by bacterial suspensions

Using gas chromatography/isotope ratio mass spectrometry to determine the fractionation factor for H2 production by hydrogenases

“…Like all catalysts, [NiFe]‐hydrogenases can catalyze both the forward and the reverse reaction, as well as a H 2 ‐H 2 O exchange reaction. All these reactions can occur even when the H 2 partial pressure is low . Thus, the isotope ratio of the H 2 in the headspace may be influenced by reactions other than the evolution reaction.…”

“…All these reactions can occur even when the H 2 partial pressure is low. [27,28] Thus, the isotope ratio of the H 2 in the headspace may be influenced by reactions other than the evolution reaction. To limit the influence of the competing reactions, an excess amount of a strong reductant (80 mM Na 2 S 2 O 4 ) was used in the experiments to maintain a large thermodynamic driving force for H 2 production and to saturate the enzyme to ensure maximal velocity.…”

“…Even under conditions in which H 2 formation is favored (e.g. very low partial pressures of H 2 or the presence of reducing agents), some H 2 uptake can be still be observed . Hydrogenases also catalyze a non‐productive H 2 ‐H 2 O exchange reaction in which the H atoms of H 2 exchange with H 2 O with no net formation or consumption of H 2 .…”

“…very low partial pressures of H 2 or the presence of reducing agents), some H 2 uptake can be still be observed. [25][26][27][28] Hydrogenases also catalyze a non-productive H 2 -H 2 O exchange reaction in which the H atoms of H 2 exchange with H 2 O with no net formation or consumption of H 2 . Because both H 2 consumption and H 2 -H 2 O exchange of H 2 will alter the isotope ratio of H 2 in the headspace, these reactions will perturb the calculated fractionation factor for H 2 formation.…”

Hydrogenase and Hydrogen Metabolism in Micrococcus Aerogenes

“…A number of bacteria containing hydrogenase, as measured by hydrogenation procedures, have been found to catalyze the exchange of deuterium with water, i.e., D2 + H20 = HD + HDO (Farkas, 1936;Hoberman and Rittenberg, 1943; Farkas and Fischer, 1947;Johnston and Frenkel, 1951;Hyndman et al, 1953). In addition, fixation of molecular tritium by a variety of bacteria has been demonstrated by Smith and Marshall (1952).…”