LIGHT-INDUCED REDUCTION OF NITRATE, NITRITE AND HYDROXYLAMINE IN A BLUE-GREEN ALGA, ANABAENA CYLINDRICA

1. Reduction of nitrate, nitrite and hydroxylamine by intact cellsof Anabaena cylindrica was investigated with special referenceto the stimulating effect of light on these processes.
2. Itwas found that in light and under anaerobic condition thesecompounds are reduced to ammonia, with the production of extraoxygen. The stoichiometry of the reactions under these conditionscan be represented as follows: HNO₂+H₂O=NH₂+2O₂ HNO₂+H₂O=NH₂+1O₂ NH₂OH+H₂O=NH₂+O₂+H₂O
3. Reduction of nitrite and hydroxylaminewas markedly suppressedby CMU in the light but not in the dark.KCN inhibited reductionto the same extent both in the lightand in the dark. Reductionin the light was much less sensitiveto the uncoupling agent,DNP, than was that in the dark.
4. Atlow light intensities, CO_2– was suppressed by 20–30per cent by the simultaneous provision of nitrite, but the nitritereduction was not affected at all by CO₂. At high light intensities,reduction of nitrate and nitrite was considerably acceleratedby CO₂
5. On the basis of these findings, a possible mechanismfor thelight stimulation of the reactions in question was brieflydiscussed.

(Received August 22, 1962; )