Reflecting the increasingly common analogies between computer science and biology in the 1960s, Rodbell believed that the fundamental information processing systems of both computers and biological organisms were similar. He asserted that individual cells were analogous to cybernetic systems made up of three distinct molecular components: discriminators, transducers, and amplifiers (otherwise known as effectors). The discriminator, or cell receptor, receives information from outside the cell; a cell transducer processes this information across the cell membrane; and the amplifier intensifies these signals to initiate reactions within the cell or to transmit information to other cells.
In December 1969 and early January 1970, Rodbell was working with a laboratory team that studied the effect of the hormone glucagon on a rat liver membrane receptor—the cellular discriminator that receives outside signals. Rodbell discovered that ATP (adenosine triphosphate) could reverse the binding action of glucagon to the cell receptor and thus dissociate the glucagon from the cell altogether. He then noted that traces of GTP (guanosine triphosphate) could reverse the binding process almost one thousand times faster than ATP. Rodbell deduced that GTP was probably the active biological factor in dissociating glucagon from the cell's receptor, and that GTP had been present as an impurity in his earlier experiments with ATP. This GTP, he found, stimulated the activity in the guanine nucleotide protein (later called the G-protein), which, in turn, produced profound metabolic effects in the cell. This activation of the G-protein, Rodbell postulated, was the "second messenger" process that Earl W. Sutherland had theorized. In the language of signal transduction, the G-protein, activated by GTP, was the principal component of the transducer, which was the crucial link between the discriminator and the amplifier. Later, Rodbell postulated, and then provided evidence for, additional G-proteins at the cell receptor that could inhibit and activate transduction, often at the same time. In other words, cellular receptors were sophisticated enough to have several different processes going on simultaneously.
Svoboda, P (June 1995). "[The Nobel Prize for physiology and medicine 1994. Alfred G. Gilman and Martin Rodbell--the role of GTP-binding proteins in signal transfer in the interior of cells]". Cas. Lek. Cesk.134 (13). Czech Republic: 415–7. ISSN0008-7335. PMID7671286.
Bogucki, W M (1995). "[Nobel prize in physiology and medicine in the year 1994]". Pneumonologia I Alergologia Polska. 63 (1–2). Poland: 120–2. ISSN0867-7077. PMID7633362.
Fredholm, B B; Aperia A (October 1994). "[Nature's solution of the communication problem resulted in Nobel Prize. Significance of G-proteins for signal transmission in cells]". Läkartidningen. 91 (42). Sweden: 3811–7. ISSN0023-7205. PMID7996951.
