How were signal transduction pathways discovered?
Signal transduction involves the binding of extra cellular signalling molecules, to receptors that trigger events inside the cell.
In 1970 Martin Rodbell examined the effects of glucagon on a rat's liver cell membrane receptor. He noted that guanosine triphosphate disassociated glucagon from this receptor and stimulated the G - protein , which strongly influenced the cells metabolism. Thus it was deduced that the G protein is a transducer that accepts glucose molecules and affects the cell.
For this he shared the 1994 Nobel Prize in Physiology and Medicine with Alfred G. Gilman.