Observations on the binding of adenosine 3':5'-monophosphate to cell membrane fragments from ox cerebral cortex.

Microsomal or synaptosome membrane fragments from ox brain bind cyclic AMP with a pH optimum of 7.0. Scatchard analysis shows the presence of at least two binding sites. Cyclic GMP and cyclic IMP only inhibit binding at concentrations 5000 times that of cyclic AMP and even higher concentration ratios of ATP and AMP have no effect. Membrane fragments saturated with cyclic [3-H]AMP lost less than 7% of bound nucleotide on incubation at 0 degrees C for 45 min but lost 25 % in the same period in the presence of 10 muM non-radioactive cyclic AMP.