| Abstrakt: |
Acetylene reduction, deuterium uptake and hydrogen evolution were followed in in-vivo cultures of Azospirillum brasilense, strain Sp 7, by a direct mass-spectrometric kinetic method. Although oxygen was needed for nitrogenase functioning, the enzyme was inactivated by a fairly low oxygen concentration in the culture and an equilibrium had to be found between the rate of oxygen diffusion and bacterial respiration. A nitrogenase-mediated hydrogen evolution was observed only in the presence of carbon monoxide inhibiting the uptake hydrogenase activity which normally recycles all the hydrogen produced. However, under anaerobic conditions and in the presence of deuterium, a bidirectional hydrogenase activity was observed, consisting in D2 uptake and in H2 and HD evolution. In contrast to the nitrogenase-mediated H2 production, this anaerobic H2 and HD evolution was insensitive to the presence of acetylene and was partly inhibited by carbon monoxide. It was moreover relatively unaffected by the deuterium partial pressure. These results suggest that the anaerobic H2 and HD evolution can be ascribed to a reverse hydrogenase activity under conditions where D2 is saturating the uptake process and scavenging the electron acceptors. Although the activities of both nitrogenase and hydrogenase were thus clearly differentiated, a close relationship was found between their respective functioning conditions. |
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