Ionomycin is a very long-chain fatty acid, docosa-10,16-dienoic acid, substituted with methyl groups at positions 4, 6, 8, 12, 14, 18, and 20; hydroxy groups at positions 11, 19, and 21; and a (2',5-dimethyloctahydro-2,2'-bifuran-5-yl)ethanol group at position 21. Produced by *Streptomyces conglobatus*, it functions as a calcium ionophore, raising intracellular Ca²⁺ levels and serving as a research tool to study Ca²⁺ transport across biological membranes. It is classified as a metabolite, enol, cyclic ether, very long-chain fatty acid, and polyunsaturated fatty acid.