Summary: The cyanobacterium grown in light-limited and CO-limited chemostat cultures showed varying rates of CO fixation with peaks at dilution rates of 0.10 to 0.12 h. 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 CO-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 CO-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 can selectively express different enzymes, possibly by transcriptional control.


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