Porcine proparathyroid hormone. Identification, biosynthesis, and partial amino acid sequence.

Porcine parathyroid gland slices were incubated with 3H-labeled amino acids in order to label tissue proteins. After incubation a crude hormonal extract was prepared and analyzed by chromatography on carboxymethylcellulose. Among the three radioactive peaks which were detected in the eluate, two were identified as parathyroid hormone and proparathyroid hormone. Based on thin layer gel filtration in the presence of 6 M guanidine-HCl, the proparathyroid hormone had a molecular weight of 11,500 compared to about 9600 for parathyroid hormone. Radioisotope sequence analysis of the proparathyroid hormone revealed a partial sequence of: Lys1-Pro2-Ile3-Lys4-Lys5-Arg6-Ser7-Val8-Ser9--Ile11--Met14--Gly18--Ser22--Ser23---. Thus, from position 7 onward the relative position of each amino acid tested in this molecule corresponded exactly to that in the porcine parathyroid hormone sequence. The conservation of a similar, though not identical, basic hexapeptide grouping Lys-X-Y-Lys-Lys-Arg- at the amino terminal region of the prohormone in all species examined thus far (porcine, human, and bovine) suggests that this segment of the molecule may play an important role in the conversion of the prohormone to the hormone.