ABSTRACT
This chapter focuses on both the common and divergent features of peptide hormone action and includes representative examples of the major signalling pathways. Each peptide hormone interacts with a specific high affinity receptor which is an integral protein spanning the plasma membrane. A number of novel approaches are being taken to facilitate the design of a new generation of non-peptide peptide mimetics. Polypeptides corresponding to regions of the intracellular domains of receptors have also been used to study their effect on G-protein activation in the absence of intact receptor. An additional way in which the magnitude and duration of G-protein-mediated signals can be controlled is by downregulation of the particular G-protein itself. The identification of multiple protein isoforms at each step of each signal transduction pathway has advanced an explanation for the diverse effects which can be elicited by a particular hormone in a given cell/tissue context.
