Cyclic Amp: A Naturally Occurring Acrasin in the Cellular Slime Molds

There has been a long search for the chemical identity of acrasin, the chemotactic substance responsible for the aggregation of amoebae in the development of cellular slime molds. With the help of a new, quantitative assay, it was possible to show that supernatants from the bacterium Escherichia coli contained an attractant for the amoebae of Dictyostelium discoideum, and now it is known that this attractant is cyclic 3', 5'-AMP. Furthermore, we have evidence that cyclic AMP is synthesized by the related species Polysphondylium pallidum. It is also known that D. discoideum synthesizes an attractant, but as yet we have not been able to obtain large enough quantities for chemical analysis. This appears to be due to the secretion by the amoebae of large quantities of a phosphodiesterase that specifically breaks down the cyclic 3', 5'-AMP acrasin to 5'-AMP. In mammals, from the work of Sutherland and his collaborators, it is known that cyclic AMP is a second messenger in hormone reactions. It is suggested that in the more primitive cellular slime molds, cyclic AMP serves as a primary messenger.