CALCIUM‐BINDING PHOSPHOPROTEIN OF PIG BRAIN: EFFECTS OF CATIONS ON THE CALCIUM BINDING

—The effects of various cations on the calcium‐binding properties of a brain phosphoprotein have been investigated employing an ultrafiltration binding assay. Sodium, magnesium, barium, strontium and manganese ions were competitive inhibitors of the calcium binding, and their affinity for the calcium‐binding site increased in the order given. Potassium was a non‐competitive inhibitor. Lanthanum, lead, mercuric and cadmium ions precipitated the phosphoprotein from solution. These findings are discussed in relation to a postulated role for the protein as a calcium‐receptor molecule involved in release of neurotransmitters.