Cyclic AMP binding proteins in early embryos of Drosophila melanogaster.

A variety of effects of cyclic AMP on cellular and subcellular phenomena suggest that there may be other modes of action of cyclic AMP then activation of protein kinase. It is also known that developing embryos contain cyclic AMP and its related enzymes. In order to explore the role of cyclic AMP in embryogenesis, a survey of proteins capable of binding cyclic AMP in the embryonic supernatant of Drosophila melanogaster was carried out. As the result, two cyclic AMP-binding proteins were found and characterized. The one (L) is, as expected, associated with protein kinase and has a dissociation constant of about 10(-9) M. Its molecular weight of 21 000 daltons is extremely small when compared with similar proteins in other organisms. The other (H), whose function is yet to be found, has a molecular weight of about 200 000 daltons and has a dissociation constant of about 10-7 M. Some laxity in binding specificity of the latter protein among adenosine nucleotides was observed, but cyclic AMP is the strongest ligand among them.