Subcellular Location of Human Parathyroid Hormone Immunoreactive Peptides and Preliminary Evidence for a Precursor to Human PTH 1

Abstract

In 1963, Berson, Yalow, Aurbach and Potts reported the development of a radio-immunoassay for parathyroid hormone (PTH) (1). Even though this tool has been available for several years, the nature of the processes of synthesis, storage and secretion of PTH is incompletely understood. Evidence of a possible precursor in the biosynthesis of PTH has been shown by both Cohn et al. (2) and Kemper et al. in the cow (3), and by Habener et al. (4) and Chu et al. (5), in the human.

This communication will show evidence for the existence of multiple immunoreactive human PTH polypeptides in parathyroid glands, two of which appear to be larger than the previously described precursors to PTH. Furthermore, we will show the intracellular location of these polypeptides. These data provide a basis for formulation of a hypothesis that may explain the interrelationships of these polypeptides.

Methods. Preparation of subcellular fractions. The subcellular distribution of immunorea ctive PTH (iPTH) was studied in human parathyroid tissue surgically obtained from a patient with severe secondary hyper-parathyroidism due to chronic renal failure, and from another with a large parathyroid adenoma. A portion of the glands was immediately chilled, weighed and homogenized in 10 ml of 0.25 M sucrose at 0°. A one ml aliquot of the homogenate was removed; the remaining suspension was carried through differential centrifugation to obtain subcellular fractions. The speeds and times for centrifugation were identical to those we have used with parathyroid tissue and are described in detail elsewhere (6).

Radioimmunoassay for parathyroid hormone. PTH was assayed by a double antibody method similar to that originally described by Morgan and Lazarow (7) for separation of bound, from free, tracer. The chicken antibody to bovine PTH (bPTH), designated C-12, and another chicken anti-bPTH, designated C-14, were gifts from Dr. Claude Arnaud of the Mayo Clinic, Rochester, MN, and were used in our initial studies.