Intracellular Processing and Secretion of Parathyroid Gland Proteins

Abstract

Publisher Summary This chapter focuses on parathyroid hormone (PTH), its synthesis, intracellular processing, and secretion, and provides current information on the chemistry and biology of secretory protein-I (SP-I) and its possible relationship to PTH. The parathyroid gland is important in fields related to calcium metabolism because of the role played by its hormone PTH plays in the regulation of body calcium. The chapter also focuses on the gland because of the realization that it also synthesizes and secretes a major glycoprotein termed SP-I that is similar to chromogranin A (CGA), a protein co-secreted with epinephrine by the adrenal. SP-I/CGA appears to be present in a large number of endocrine, but not exocrine, cells. PTH is unglycosylated and generally does not contain modified amino acids. PTH exhibits a complex conformation in solution that appears to reorder at different pHs. Images of PTH examined by dark-field electron microscopy suggest that the molecule consists of two domains connected by a short stalk. The fundamental mechanisms responsible for secretory control are at least as complex as those regulating intracellular formation and processing of the hormone.