title: Binding of calcium to the proteolipid phosphorin.
abstract: Phosphorin is a phosphate-binding proteolipid isolated from rabbit kidney brush border membrane vesicles that binds inorganic phosphate with high affinity and specificity. This binding of phosphate has a Hill coefficient of 1.92 and an absolute requirement for the presence of a divalent metal. We now describe the binding of Ca2+ to phosphorin that had been depleted of endogenous divalent metal. The dependence of the binding of Ca2+ over the concentration range of 5-100 microM produced a sigmoidal curve, yielding a Hill coefficient of 2.46. (Ruthenium red and La3+ were also potent inhibitors of Ca2+ binding). The divalent metals Mn2+ and Mg2+ were able to inhibit binding of Ca2+ and produced Hill coefficients of 1.75 and 1.98; however, Ba2+ and Sr2+ were less effective in their ability to inhibit binding. In addition, the amine-reactive reagent, 4,4'-diisothiocyano-2,2'-disulfonic acid (DIDS), which had previously been found to inhibit binding of phosphate to phosphorin, also completely inhibited binding of Ca2+. We propose that a phosphorin-Me2+ complex forms the molecular species that binds phosphate.
authors: Department of Medicine, University of California, San Diego, La Jolla.
authors: R J
authors: RJ
authors: Kessler
authors: D A
authors: DA
authors: Vaughn
authors: D D
authors: DD
authors: Fanestil
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008345:Manganese / Q000494:pharmacology; D010710:Phosphates / Q000378:metabolism*; D011510:Proteolipids / Q000302:isolation & purification / Q000378:metabolism*; D011817:Rabbits; D012430:Ruthenium Red / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D010710:Phosphates; D011510:Proteolipids; C036541:phosphate-binding proteolipid; D012430:Ruthenium Red; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D008345:Manganese; D008274:Magnesium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; D002118:Calcium