Calcium-binding proteins in the parathyroid gland. Detailed studies of parathyroid secretory protein.
In order to identify calcium (Ca2+)-binding proteins in the parathyroid gland, we used electrophoretic blots of proteins separated by a two-dimensional nondenaturing/denaturing gel system and incubated them with 45Ca2+. Parathyroid secretory protein (PSP) and proteins with approximate molecular weights of 98,000, 88,000, 58,000, and 30,000 were noted to bind Ca2+ in cytosolic fractions from bovine parathyroid, adrenal, and pituitary glands. However, differences in the binding affinity and capacity of the various proteins were observed. PSP displayed a low affinity and high binding capacity for Ca2+. In the presence of 5 mM MgCl2 and 60 mM KCl, native PSP (immobilized on nitrocellulose filters) bound 7.5 mol of Ca2+/mol of protein monomer with an apparent Kd of 1.1 mM. Immunoblotting identified the association of PSP with parathyroid cell membranes in a Ca2+-dependent manner. This property, together with its heat stability, distinguished PSP from other cytosolic Ca2+-binding proteins which were identified. There was also evidence for a Ca2+-dependent protein-protein interaction (aggregation) of PSP present in a Nonidet P-40 extract of cell membranes. The high Ca2+ binding capacity of PSP and its Ca2+-dependent membrane association may be features that make PSP a potentially important protein in secretory cells.
Leiser
M
M
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461.
Sherwood
L M
LM
D000311:Adrenal Glands / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000302:isolation & purification* / Q000378:metabolism; D002417:Cattle; D053379:Chromogranin A; D002864:Chromogranins; D003600:Cytosol / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D007700:Kinetics; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism; D008970:Molecular Weight; D010280:Parathyroid Glands / Q000378:metabolism*; D010902:Pituitary Gland / Q000378:metabolism
D002135:Calcium-Binding Proteins; D053379:Chromogranin A; D002864:Chromogranins; D008565:Membrane Proteins; D002118:Calcium