<P> In mitochondria the terminal membrane complex (Complex IV) is cytochrome oxidase . Aerobic bacteria use a number of different terminal oxidases . For example, E. coli does not have a cytochrome oxidase or a bc complex . Under aerobic conditions, it uses two different terminal quinol oxidases (both proton pumps) to reduce oxygen to water . </P> <P> Anaerobic bacteria, which do not use oxygen as a terminal electron acceptor, have terminal reductases individualized to their terminal acceptor . For example, E. coli can use fumarate reductase, nitrate reductase, nitrite reductase, DMSO reductase, or trimethylamine - N - oxide reductase, depending on the availability of these acceptors in the environment . </P> <P> Most terminal oxidases and reductases are inducible . They are synthesized by the organism as needed, in response to specific environmental conditions . </P> <P> Just as there are a number of different electron donors (organic matter in organotrophs, inorganic matter in lithotrophs), there are a number of different electron acceptors, both organic and inorganic . If oxygen is available, it is invariably used as the terminal electron acceptor, because it generates the greatest Gibbs free energy change and produces the most energy . </P>

Where are the proteins of the electron transport chain embedded