C 02 Fixation in A nabaena cylindrica

14C 0 2 Fixation, Effect of Iodoacetamide, Glycolate Metabolism, Anabaena The cyanobacterium Anabaena cylindrica grown in a nitrogen free medium at + 25 °C was used for short-term 1 4C-kinetics experiments under different conditions. During the dark/light transients the initial fixation products were mainly sugar monophosphates and 3-phosphoglyceric acid (Calvin cycle intermediates), aspartate (10% of total radioactivity) and glycine/serine. Io­ doacetamide (0.01 m) caused an inhibition of photosynthetic 1 4C 0 2 fixation and a ^ -incorpor­ ation into aspartate, glutamate and 3-phosphoglyceric acid only. During dark 1 4C 0 2 assimilation labelling of these products could be measured, too. In a nitrogen atmosphere (N 2 + 0.04 vol. % C 0 2) a strong labelling of sugar monophosphates mainly at the beginning of photosynthetic period could be observed. In an oxygen atmosphere (100% 0 2) an enhanced label of aspartate and glycerate and a decreased radioactivity in sugar monophosphates were found. Our results were discussed with reference to the operating of a phosphoenolpyruvate carboxylation reaction be­ sides the Calvin cycle and to the glycolate metabolism.