Proparathyroid hormone: identification of a biosynthetic precursor to parathyroid hormone.

Biosynthesis of a precursor to bovine parathyroid hormone has been demonstrated in slices of parathyroid tissue incubated in vitro. The proparathyroid hormone is 15-20 amino acids larger than the bovine hormone, and has a molecular weight of about 11,500 as determined by polyacrylamide gel electrophoresis. Upon incubation of parathyroid slices with [(14)C]aminoacids, radioactivity is detected initially in the precursor. If incorporation of [(14)C]aminoacids is inhibited after a short incubation either by replacement of radioactive amino acids with unlabeled amino acids or by addition of puromycin, the amount of radioactivity in the precursor decreases, while the radioactivity in the hormone continues to increase. The precursor is bound by an antibody that is specific for parathyroid hormone, and its binding can be inhibited by addition of the hormone. Analysis of tryptic digests indicates that the precursor and the hormone have common tryptic peptides, and that there are at least two additional peptides in the precursor.