Two acidic Ca2+ -binding proteins (CaBP33 and CaBP37) purified from bovine brain have been characterized in terms of immunological properties, heat-sensitivity, electrophoretic mobility, and Ca2+-dependent binding to negatively charged phospholipids and to brain membranes. They were induced to bind to membranes by homogenization of brain tissue in the presence of CaCl2. The membrane-bound CaBP33/CaBP37 mixture resisted extraction with detergents and was solubilized with high concentrations of EGTA/KC1. However, apparent Ca2+-independent binding of the two proteins to membranes seemed to occur as well. This latter fraction of membrane-bound CaBP33 and CaBP37 could be solubilized with Triton X-100, indicating that brain membranes normally contain the two proteins as intrinsic components.
