Cytochrome C' (1BBH) - Cytochromes are proteins that act as carriers of electrons - they transfer electrons from a doner to an acceptor. "Chains" of cytochromes and other electron transporters are found in the inner membranes of mitochondria and chloroplasts, and in bacterial membranes. While electrons are transferred laterally through the membrane (downhill energetically), protons are transported across the membrane (uphill energetically). The total energy lost by the electrons must be more than that gained by the protons to satisfy the Second Law of Thermodynamics. As protons accumulate on one side of the membrane a pH gradient is formed across the membrane. This pH gradient can then be used to do work such as ATP synthesis.

In this view of a cytochrome C' dimer from the bacterium Chromatium vinosum. the polypeptide chains are highlighted on the left illustrating the alpha helices. The cleft or space between the helices of each of the two subunits is occupied by a heme group. The right view (same orientation) illustrates the protein with the subunits and hemes highlighted in different colors. Hemes contain an iron atom at their center which is the actual site of reduction (as electrons are acccepted) and oxidation (as electrons are given up). The polypeptide chain holds the hemes in the correct orientation relative to the donor and acceptor molecules.

8/22/04 Copyright (C) 2004, Jonathan Monroe, monroejd@jmu.edu. All rights reserved.
URL: http://csm.jmu.edu/biology/courses/bio220/cytc.html