Divalent cation ionophore A23187 forms lipid soluble complexes with leucine and other amino acids

THE Streptomyces antibiotic A23187, a divalent cation ionophore1, has been used as a tool in studies of the role of calcium in several cellular phenomena2–5. A23187 has a much higher affinity for divalent than monovalent cations, and the increased permeability induced by this ionophore in cellular membranes favours calcium and magnesium. X537A, another divalent cation ionophore6, also enhances fluxes of monovalent cations7 and forms lipid-soluble complexes with noradrenaline and some other organic compounds8. A23187 has often been referred to as a specific divalent cation ionophore although, to our knowledge, the evidence for the specificity is restricted to the lack of interaction with common monovalent cations like sodium and potassium1,2. In this paper we report experiments which show that A23187 is able to form lipid-soluble complexes with leucine and other amino acids at concentrations as low as or lower than those needed to form similar complexes with calcium.