Studies on the Subcellular Localization of Proparathyroid Hormone and Parathyroid Hormone in the Bovine Parathyroid Gland: Separation of Newly Synthesized from Mature Forms1

Bovine parathyroid gland homogenates were separated by differential centrifugation into cytosol and participate fractions. Analysis for parathyroid hormone by bioassay, immunoassay and chemical isolation revealed that over 90% of the hormone was in particulate fractions. By incubating gland slices with radioactive amino acids, it was possible to distinguish newly synthesized (that is, radioactive) proPTH and PTH from those corresponding peptides which existed in the tissue prior to incubation. The results of experiments utilizing sucrose gradient centrifugation or extraction with sodium deoxycholate of the gland homogenate fractions established that, in operational terms, at least 2 particulate subpopulations which contain the hormone and prohormone exist in the cell: 1) a deoxycholateresistant fraction which contains at least threefourths of the total PTH protein and a small amount of prohormone, both of relatively low specific radioactivity; and 2) a deoxycholateextractable fraction which contains a small amount of PTH and the majority of the proPTH, both of high specific radioactivity. On the basis of the sedimentation behavior, resistance to extraction by deoxycholate, observations in the electron microscope and specific radioactivity of the hormone and prohormone, population 1 appears to represent the contents of mature secretory granules of the cell and population 2, the contents of the endoplasmic reticular space, Golgi vesicles and perhaps prosecretory granules. (Endocrinology93: 1387, 1973)