Key intracellular regulator of a number of cellular processes; found in most animal cells, in bacteria, and in some higher plants. First isoln and identification: Rall et al., J. Biol. Chem. 224, 463 (1957); Sutherland, Rall, ibid. 232, 1077 (1958). Molecular structure and conformation: Cook et al., J. Am. Chem. Soc. 79, 3607 (1957); Lipkin et al., ibid. 81, 6198 (1959); Watenpaugh et al., Science 159, 206 (1968). Syntheses: Smith et al., J. Am. Chem. Soc. 83, 698 (1961); Borden, Smith, J. Org. Chem. 31, 3247 (1966). Physical data: D. Lipkin et al., J. Am. Chem. Soc. 81, 6075 (1959). Functions as a mediator of hormone-action for a variety of hormones such as epinephrine, glucagon and ACTH, q.q.v. Activates phosphorylation of proteins by protein kinases. Defined as a “second messenger” because of its response to hormones (“first messengers”). Converted from adenosine triphosphate (ATP) by the enzyme adenylate cyclase. Deactivated by cyclic nucleotide phosphodiesterases which convert it to 5′-adenylic acid. Reviews of biochemical model: Sutherland et al., J. Biol. Chem. 237, 1220-1243 (1962); Robison et al., Annu. Rev. Biochem. 37, 149 (1968); Jost, Rickenberg, ibid. 40, 741 (1971); Sutherland, J. Am. Med. Assoc. 214, 1281 (1970); Pastan, Perlman, Nature New Biol. 229, 5 (1971); G. A. Robison et al., Eds., Ann. N.Y. Acad. Sci. 185, (1971); Losert, Pharmazie 28, 351 (1973). See also Cyclic GMP. Identity with acrasin from cellular slime molds (Dictyostelium species), where it acts as a “first” rather than a “second messenger”: Konijn et al., Proc. Natl. Acad. Sci. USA 58, 1152 (1967). Review of quantitative methods: Methods in Molecular Biology vol. 3, “Methods in Cyclic Nucleotide Research”, Mark Chasin, Ed. (Marcel Dekker, New York, 1972). Books: G. A. Robison et al., Cyclic AMP (Academic Press, New York, 1971); Advan. Cyclic Nucleotide Res. vols. 1, 2, 3, P. Greengard, G. A. Robison, Eds. (Raven Press, New York, 1972, 1973); Handb. Exp. Pharmacol. 58, “Cyclic Nucleotides”, Pt I: Biochemistry and Pt II: Physiology & Pharmacology, J. A. Nathanson, J. W. Kobabian, Eds. (Springer-Verlag, New York, 1982) 736 and 1000 pp resp.