MODES OF ELECTRON-TRANSFER FROM MOLECULAR-HYDROGEN IN ANABAENA-CYLINDRICA

Several natural and artificial electron donors were assayed in the C2H2-reduction of heterocysts isolated from the cyanobacterium Anabaena cylindrica. Among these, molecular hydrogen was the most effective one when the assays were performed in the light. The C2H2-reduction and the Knallgas reaction of intact Anabaena filaments as well as the H2-supported C2H2-reduction of isolated heterocysts were compared for their sensitivity towards several inhibitors known to affect the photosynthetic or respiratory electron flow. Among these, dibromothymoquinone (DBMIB) affected all three reactions equally indicating that plastoquinone is a common intermediate of the H2-consumptions by either the respiratory or the photosynthetic electron transport. Metronidazole inhibited the H2-utilization via photosynthesis but did not affect the consumption of this gas by respiration and therefore allows to differentiate between the two pathways of hydrogen utilization. The studies with the inhibitors are suggestive for a segment of electron carriers on the membranes common to both photosynthesis and respiration in heterocysts of Anabaena. © 1979 Springer-Verlag.