Cytochrome c reductase is a central enzyme in the electron transport chain of oxidative phosphorylation. The inhibition of this reaction disrupts the formation of the proton gradient across the inner membrane of the mitochondria. The production of ATP is subsequently inhibited, as protons are unable to flow through the ATP synthase complex in the absence of a proton gradient. This inhibition also results in the formation of the toxic free radical superoxide. In presence of antimycin A the dependence of the superoxide production rate on oxygen level is hyperbolic. In cultured cells at the background of mitochondrial respiration inhibition, the rate of superoxide production exceeds the cellular mechanisms to scavenge it, overwhelming the cell and leading to cell death. It has also been found to inhibit the cyclic electron flow within photosynthetic systems along the proposed ferredoxin quinone reductase pathway. Although cyanide acts to block the electron transport chain, Antimycin A and cyanide act in different mechanisms. Cyanide binds a site in neighboring protein where iron normally binds, preventing oxygen from binding at all. This prevents cellular respiration completely leading to cell death. Because Antimycin A binds to a specific protein in the electron transport chain, its toxicity can be highly species dependent because of subtle species specific differences in ubiquinol. This is why Fintrol can be used a selective killing agent in commercial farming. Fungus-growing attine ants have been shown to use antimycins - produced by symbiotic Streptomyces bacteria - in their fungiculture, to inhibit non-cultivar (i.e. pathogenic) fungi. One research group studying these symbiotic Streptomyces bacteria recently identified the biosynthetic gene cluster for antimycins, which was unknown despite the compounds themselves being identified 60 years ago. Antimycins are synthesised by a hybrid polyketide synthase (PKS)/non-ribosomal peptide synthase (NRPS). Toxicity Lethal Doses Lethal doses in fish and amphibian species Lethal Doses in Mammals Human Exposure and First Aid Exposure to Treated Water: The effects of chronic, sub-lethal human exposure have estimated and extrapolated from murine (=pertaining to rodents) toxicology studies. Estimates in the literature have been determined using EPA risk assessment protocols. Studies aimed at determining these levels found a concentration in mice where there is "No Observed Adverse Effect Level." From there, the EPA describes methods to determine a reference dose (RfD), the upper limit of the substance that can be consumed daily for the rest of one's life without any observable consequences. The RfD was determined to