Multiple cAMP-binding proteins in Aplysia tissues

While it is recognized that cAMP is able to regulate distinct cellular processes differentially, the molecular basis for the diversity of its effects remains unclear. Using photoaffinity labeling with 32P-8 azido-cAMP and two-dimensional gel analysis, we have identified 26 electrophoretic variants of cAMP-binding proteins in the six different tissues of the marine mollusc Aplysia californica sampled. Some of these proteins are found in most tissues, others only in a few; still others appear to be restricted to a single tissue. All of these proteins bind cAMP specifically. The two-dimensional polyacrylamide gel electrophoretic patterns of binding proteins seen in the different tissues fall into three classes. One pattern is shared by the nervous system and embryos. The second is found in muscular tissues (heart, buccal muscle, siphon, and gill). The third pattern is specific to sperm. The presence of distinct subsets of cAMP-binding proteins in different tissues suggests that at least some of the diversity in cAMP's regulatory function may result from diversity in the proteins that bind it.