Extraction, purification, and partial characterization of bovine parathyroid secretory protein

Parathyroid secretory protein (PSP) was purified from extracts of bovine parathyroid glands using radioactive PSP as a marker during purification. The labeled preparation was obtained by gel filtration of medium resulting from incubation of parathyroid glands with radioactive amino acids for 4 h. Alkaline extraction, ammonium sulfate precipitation, ion-exchange chromatography on DEAE-cellulose, and gel filtration over Bio-Gel A 1.5 M and A 5 M resulted in a homogeneous product. Purified PSP monomer had a Mr = 67,000, was highly acidic on gel electrophoresis, and contained over 35% glutamic and aspartic acid residues. Approximately 18% of the protein consisted of carbohydrate residues. The homogeneity of the final product was established by polyacrylamide and sodium dodecyl sulfate (SDS) gel electrophoresis and the identification of a single NH2-terminal leucine. A radioimmunoassay for PSP was developed to identify the protein in tissue extracts and in incubation medium. Purification of PSP should be useful in defining further its biochemistry, biologic function, and control of secretion.