THE TRANSMEMBRANE SIGNALING

The biochemical processes involved in transmission of the molecular information in cells delivered by extracellular signals (e.g. hormones, neurotransmitters, growth factors, mitogens) have been extensively studied during the last two decades. The great interest in these processes and their important role is underlined by the recognition of the substantial contributions to research in this area with the Nobel Prize awarded in 1992 to Edward H. Fischer and Edwin G. Krebs for their principal work on phosphorylation and dephosphorylation of proteins and, two years later, in 1994 to Martin Rodbell and Alfred G. Gilman, for finding and characterizing the involvement of GTP-binding proteins in the transmembrane signal transduction. To communicate with their surroundings, all cells possess the capacity and the apparatus for receiving and processing the extracellular information, but there are several mechanisms for the information signal transmission across the plasma membrane. In all of them, reversible protein phosphorylation, as a major process for the posttranslational control of protein functions (Hunter, 1991) has a prominent role in transduction of the extracellular signals into specific phosphorylation patterns of intracellular proteins in the cytoplasm and nucleus.