PARATHYROID SECRETORY PROTEIN IN KEY ENDOCRINE GLANDS

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The long-term objective of the proposed work is to discover the physiological function of a class of proteins which occur in endocrine tissues and are localized within hormone containing cells of these tissues. In the parathyroid gland this protein is called secretory protein-I (SP-I) while in the adrenal gland it is referred to as chromogranin A (Ch A). Since secretion of this protein accompanies hormone secretion from these 2 tissues it has been suggested that this may be a common feature of all endocrine tissues. We plan to test this hypothesis by examining pituitary, pancreas, and thyroid, along with adrenal and parathyroid tissues under a variety of secretory and non-secretory conditions to determine if an SP-I/Ch A protein is secreted with hormone. These studies will be done with fresh bovine tissue slices in a perifusion apparatus over a 4-5 hour period and perifusate analyzed by radioimmunoassay for SP-1/Ch A and each hormone. Since the structural information we have established for SP-I and Ch A indicate they are nearly identical homologues we also propose to isolate the SP-I/Ch A from pituitary and pancreas so that we can determine whether or not the species occurring in these tissues is chemically similar to the SP-I/Ch A of parathyroid/adrenal. These comparisons will be made by performing enzymatic and chemical digestions of the pituitary and pancreatic proteins followed by HPLC separation of the digests for comparison to the maps of similar digest obtained from the parathyroid and adrenal proteins. In addition, we will perform amino acid analysis of the separated polypeptides for further comparison. Finally, we will characterize the poorly understood Ca++ -dependent proteolysis of SP-I/Ch A which occurs in broken cell preparations. Such characterization will be approached by a) establishing the specific requirements of the proteolysis and examining the resulting products; b) determining whether or not such proteolysis occurs intracellularly to produce similar products; c) determining whether or not forms of SP-I/Ch A which are secreted bear any relationship to proteolytic products. These studies (b & c) will be conducted using dispersed parathyroid cells and radioactive amino acids to label the SP-I along with gel electrophoresis and HPLC separation to analyze forms of SP-I. Isolated lysates of chromaffin granules will be utilized for part a.