XAS Studies on the Cu_A Centers of Heme-Copper Oxidases and Loop-Directed Mutants of Azurin: Implications for Redox Reactivity

The heme-copper oxidases (historically termed cytochrome oxidases) are ubiquitous in both prokaryotic and eukaryoric aerobic organisms. They function to catalyze the 4-proton, 4-electron reduction of dioxygen to water and transduce the energy made available from O-O bond cleavage to the translocation of an additonal 4 protons across the cytoplasmic or mitochondrial membrane. The energy released is stored as an electrochemical gradient and utilized to drive ATP synthesis in the process known as oxidative phosphorylation. For these reasons reasons, heme-copper oxidases are arguably the most important enzymes in mammalian cells, providing the energy for most metabolic processes and consuming 80-90% of the oxygen we breathe.