A23187 or calcimycin a toxic and weakly antibiotic substance isolated from cultures of Streptomyces chartreusensis. It is a lipophilic 523 Da monocarboxylic acid of complex structure, two molecules of which form stable lipid-soluble complexes at pH 7.4 with one atom of certain divalent metal cations, especially Mn2+, Ca2+, and Mg2+; monovalent cations are bound only weakly. It also forms lipid-soluble complexes with certain amino acids. It is used experimentally as a calcium ionophore.
