  Mitochondria are the power house of living cells, where the synthesis of the
chemical "energy currency" adenosine triphosphate (ATP) occurs. Oxidative
phosphorylation by a series of membrane protein complexes I to IV, that is, the
electron transport chain, is the source of the electrochemical potential
difference or proton motive force (PMF) of protons across the inner
mitochondrial membrane. The PMF is required for ATP production by complex V of
the electron transport chain, i.e. by FoF1-ATP synthase. Destroying cytochrome
C oxidase (COX; complex IV) in Photodynamic Therapy (PDT) is achieved by the
cationic photosensitizer Pt(II)-TMPyP. Electron microscopy revealed the
disruption of the mitochondrial christae as a primary step of PDT. Time
resolved phosphorescence measurements identified COX as the binding site for
Pt(II)-TMPyP in living HeLa cells. As this photosensitizer competed with
cytochrome C in binding to COX, destruction of COX might not only disturb ATP
synthesis but could expedite the release of cytochrome C to the cytosol
inducing apoptosis.
