抄録
Calcium-binding protein was separated from rat milk by gel filtration, followed by ion-exchange chromatography using a DEAE-Sephadex A-25 column and characterized partially. Rat milk calcium-binding protein (mCaBP) has a molecular weight of about 16, 000 as measured by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and about 34, 000 by gel filtration using a Sephadex G-75 column. This protein specifically bound calcium with high affinity (Kd=1.45×10-6M). The mobility of mCaBP in regular PAGE was accelerated by the presence of EGTA and was delayed by calcium binding. Divalent cations such as Sr, Cd, and Mn produced an effect similar to that of calcium on the mobility of PAGE, but Zn and Fe did not. Ca-bound mCaBP was heat-stable and resistant to digestion by trypsin. These results indicate that the mCaBP undergoes a conformational change by the binding of calcium and other metal ions. The rat mCaBP was immunologically different from bovine mCaBP and human mCaBP. The properties of rat mCaBP are very similar to those of bovine mCaBP, except that it is a glycoprotein containing about 5% carbohydrates.
