Identification of a novel calcium binding protein from bovine brain

A novel Ca2+ binding protein, named caligulin, was extracted from the heat-treated 100 000 X g supernatant of bovine brain and purified to electrophoretic homogeneity. The apparent Mr of caligulin determined on sodium dodecyl sulfate polyacrylamide gels was 24000. Analysis by gel filtration chromatography indicated an apparent Mr of 33000, suggesting a monomeric protein. Amino acid composition data demonstrated the presence of 25% acidic residues, 12% basic residues and 10% leucine. In the presence of 1 mM MgCl2 and 0.15 M KCl, caligulin bound 1 mol Ca2+/mol protein with half-maximal binding at about 0.2 microM Ca2+.