Two novel brain proteins, CaBP33 and CaBP37, are calcium‐dependent phospholipid‐ and membrane‐binding proteins

Abstract
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.