Proton nuclear magnetic resonance studies on cyclic nucleotide binding to the Escherichia coli adenosine cyclic 3',5'-phosphate receptor protein

A ‘H NMR study on the Escherichia coli aden-osine cyclic 3’,5’-phosphate receptor protein (CRP) alone and in its complexes with adenosine cyclic 3‘,5‘-phosphate (CAMP), guanosine cyclic 3’,5’-phosphate (cGMP), and a number of analogues is presented. Five sets of imidazole proton reso-nances are seen, corresponding to the five histidines per subunit found by amino acid analysis [Anderson, W. B., Schneider,