<P> Some dehydrogenases are proton pumps; others are not . Most oxidases and reductases are proton pumps, but some are not . Cytochrome bc is a proton pump found in many, but not all, bacteria (it is not found in E. coli). As the name implies, bacterial bc is similar to mitochondrial bc (Complex III). </P> <P> Proton pumps are the heart of the electron transport process . They produce the transmembrane electrochemical gradient that enables ATP Synthase to synthesize ATP . </P> <P> Cytochromes are pigments that contain iron . They are found in two very different environments . </P> <P> Some cytochromes are water - soluble carriers that shuttle electrons to and from large, immobile macromolecular structures imbedded in the membrane . The mobile cytochrome electron carrier in mitochondria is cytochrome c . Bacteria use a number of different mobile cytochrome electron carriers . </P>

Where do protons build up in the electron transport chain