Cyclic GMP and cyclic AMP binding proteins in Myxococcus xanthus

Three binding proteins, one specific for guanosine 3′: 5′-monophosphate (cGMP) and two specific for adenosine 3′: 5′-monophosphate (CAMP) have been partially purified from vegetative cells of Myxococcus xanthus M300. The cGMP binding activity was found in the periplasmic shock fluid. Scatchard analysis indicated only a single class of binding sites with high affinity (apparent KD, 42 nM). The two cAMP binding activities were physically distinct, as indicated by their elution patterns from DEAE-cellulose, KD values and cellular locations. The cytoplasmic cAMP binding protein, which is probably identical to that previously isolated from developing myxospores of M. xanthus had an apparent KD of 57 nM, whereas the periplasmic cAMP binding protein had an apparent KD of 1 PM. During development, the nucleotide binding proteins exhibited changes in activities consistent with their postulated roles during fruiting body development.