n. 1. one of several antibiotic substances produced by several species of Streptomyces, active against various fungi. They are used only experimentally, not in medicine. The two best-known antimycins are antimycin A₁ (C28H40N2O9) and antimycin A₃ (C26H36N2O9). They are notable for their mechanism of action, interference with the proton pumping mechanism of fungi. [ WordNet 1.5 +PJC ]