CoA + 2 oxidized [2Fe-2S]-[ferredoxin] + pyruvate = acetyl-CoA + CO2 + H(+) + 2 reduced [2Fe-2S]-[ferredoxin] 3-methyl-2-oxobutanoate + CoA + 2 oxidized [2Fe-2S]-[ferredoxin] = 2-methylpropanoyl-CoA + CO2 + H(+) + 2 reduced [2Fe-2S]-[ferredoxin] Heterotetramer of one alpha, one beta, one delta and one gamma chain.