[cAMP-dependent protein phosphorylation and its regulatory role in the cell]

Literary data are reviewed on the role of the cAMP-dependent phosphorylation of proteins in the regulation of cell metabolism, membrane permeability, and muscle contraction. It is suggested that a low cAMP level in the tumor and other actively proliferating cells may be associated with a raised exit of cAMP from cells into the surrounding medium because of the increased phosphorylation of the membrane proteins of these cells.