Enzymes of the Calvin Cycle and Intermediary Metabolism in the Cyanobacterium Anacystis nidulans Grown in Chemostat Culture

The cyanobacterium Anacystis nidulans grown in light-limited and CO2-limited chemostat cultures showed varying rates of CO2 fixation with peaks at dilution rates of 0·10 to 0·12 h−1. The specific activities of a number of enzymes of the reductive and oxidative pentose phosphate and glycolytic pathways and the tricarboxylic acid and glyoxylate cycles varied significantly as a function of the growth environment (substrate limitation) and organism growth rate. Ribulose-1,5-bisphosphate carboxylase varied 15-fold under CO2-limited conditions but did not change under light-limited conditions. With the exception of phosphoribulokinase, all enzymes which showed a change in specific activity increased with decreasing dilution rate. The specific activities of glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, hexokinase, ribulose-1,5-bisphosphate carboxylase and malate dehydrogenase were significantly higher in organisms grown under CO2-limited conditions than under light-limited conditions. Fructose-1,6-bisphosphate aldolase and phosphoribulokinase specific activities were similar at all growth rates and under both limitations. Isocitrate lyase was the only enzyme examined which showed higher specific activities under light-limited conditions. Thus Anacystis nidulans can selectively express different enzymes, possibly by transcriptional control.