Purification and characterization of the 27,000 Da calcium-binding protein of bovine brain.
A Ca2+-binding protein named CAB-27 was purified from bovine brain 100,000 g supernatant. The protein has a molecular mass of 27,000 Da as determined by SDS/polyacrylamide-gel electrophoresis and 35,500 Da by sedimentation-coefficient and Stokes-radius analysis. The protein contains about 26% Glx and Asx and 13% basic residues. The acidic nature of the molecule is confirmed by its pI of 4.80. In the presence of 3 mM-MgCl2 and 150 mM-KCl, CAB-27 binds 2.0 mol of Ca2+/mol of protein, with an apparent Kd of 0.2 microM. Ca2+-binding is unaffected by prior incubation of the protein at 80 degrees C for 2 min. Brain contains about 130 mg of CAB-27/kg. Immunoblotting identified CAB-27 in several bovine tissues; it appears to be particularly rich in brain and kidney. In addition, CAB-27 is identified as an inhibitor of bovine pancreas phospholipase A2 in vitro. The inhibitory activity of CAB-27 was 20-fold less potent than lipocortin. On the basis of the Ca2+-binding properties, intracellular concentration and tissue distribution of this protein, we suggest that CAB-27 may be an important intracellular Ca2+ receptor.
Tokuda
M
M
Department of Medical Biochemistry and Cell Regulation Group, University of Calgary, Alberta, Canada.
Khanna
N C
NC
Waisman
D M
DM
D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D002417:Cattle; D002848:Chromatography, DEAE-Cellulose; D002850:Chromatography, Gel; D004586:Electrophoresis; D008970:Molecular Weight; D010741:Phospholipases A / Q000037:antagonists & inhibitors; D054467:Phospholipases A2; D014018:Tissue Distribution
D000596:Amino Acids; D002135:Calcium-Binding Proteins; C043697:calcium-binding protein (brain); D010741:Phospholipases A; D054467:Phospholipases A2; D002118:Calcium