Uptake of Cyclic AMP by Natural Populations of Marine Bacteria

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Abstract
The major objective of this study was to describe the mechanism(s) of cAMP uptake by natural populations of marine bacteria. A second objective was to determine whether this uptake could contribute to the intracellular regulatory pool of cAMP. Using high-specific-activity 32P-labeled cAMP, several high-affinity uptake systems were found. The highest-affinity system had a half-saturation constant of < 10 pM. This system was extremely specific for cyclic nucleotides, particularly cAMP. It appeared to meet the criteria for active transport. Uptake of cAMP over a wide concentration range (up to 2 .mu.M) showed multiphasic kinetics, with half-saturation constants of 1 nM and greater. These lower-affinity systems were much less specific for cyclic nucleotides. Although much of the labeled cAMP taken up by the high-affinity systems was metabolized, some remained as intact cAMP within the cells during 1 h of incubation. This suggests that at least some of the bacteria use cAMP dissolved in seawater to augment their intracellular pools.