Abstract
Abstract The cyanobacterium Anabaena cylindrica grown in a nitrogen -free medium at + 25 °C was used for short-term 14C-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 м) caused an inhibition o f photosynthetic 14CO2 fixation and a 14C-in corporation into aspartate, glutamate and 3-phosphoglyceric acid only. During dark 14CO2 assimilation labelling of these products could be measured, too. In a nitrogen atmosphere (N2 + 0.04 vol. % CO2) a strong labelling of sugar monophosphates mainly at the beginning o f photosynthetic period could be observed. In an oxygen atmosphere (100% O2) 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.
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