Effect of Ammonia on Dark CO2 Fixation by Anabaena Cells Treated with Methionine Sulfoximine

Dark CO2 fixation by Anabaena cylindrica was stimulated about three-fold by the addition of NH4Cl to the cells. The 14CO2 incorporation experiments showed that 14C is most rapidly incorporated into aspartate and then glutamine by adding NH4CI. Glutamine accumulated predominantly after the addition of NH4Cl showing that NH4 is incorporated into glutamine by glutamine synthetase. The stimulating effect of NH4Cl on CO2 fixation and amino acid synthesis was suppressed by methionine sulfoximine, an inhibitor of glutamine synthetase. It was suggested that dark CO2 fixation was stimulated by the action of glutamine synthesis which is enhanced by ammonia.