Effect of nitrogen starvation on the level of adenosine 3′,5′-monophosphate in Anabaena variabilis

Low levels of adenosine 3′,5′-monophosphate (cyclic AMP) were detected in the cyanobacterium Anabaena variabilis using a protein binding assay and two radioisotopic labelling methods. The basal concentration of intracellular cyclic AMP ranged from 0.27 pmol/mg protein in A. variabilis Kutz grown under heterotrophic conditions to 1.0–2.7 pmol/mg protein in A. variabilis strain 377 grown autotrophically. Extracellular cyclic AMP was found to comprise as much as 90% of the total cyclic AMP in rapidly growing cultures. When A. variabilis strain 377 was starved of nitrogen, a 3–4-fold increase in intracellular cyclic AMP was observed during the 24 h period coincident with early heterocyst development.