Iron also superoxide dismutases

The synthesis of ROS can be catalyzed by iron ions, for example. Reaction of O2 with FMN or FAD (see p. 32) also constantly produces ROS. By contrast, reduction of O2 by cytochrome c-oxidase (see p. 140) is clean, as the enzyme does not release the intermediates. In addition to antioxidants (B), enzymes also provide protection against ROS superoxide dismutase [1] breaks down ( dispropor-tionates ) two superoxide molecules into O2 and the less damaging H2O2. The latter is in turn disproportionated into O2 and H2O by heme-containing catalase [2]. 

In addition to its previously mentioned role in copper transport, ceruloplasmin is an amine oxidase, a superoxide dismutase, and a ferrooxidase able to catalyze the oxidation of Fe2+ to Fe3+. Ceruloplasmin contains three consecutive homologous 350-residue sequences which may have originated from an ancestral copper oxidase gene. Like ascorbate oxidase, this blue protein contains copper of the three different types. Blood clotting factors V and VIII (Fig. 12-17), and the iron uptake protein Fet3 (Section A,l) are also closely related. 

Fig. 1. Schematic overview of copper trafficking and homeostasis inside the yeast cell. The actions of Mad and Ace 1, copper-dependent metalloregulatory transcription factors, control the production of copper import [copper transporter (Ctr) and reductase (Fre)] and detoxification/sequestration [metallothionein (MT)] machineries, respectively. Three chaperone-mediated delivery pathways are shown. Atxl shuttles Cu(I) to the secretory pathway P-type ATPase Ccc2 (right). CCS delivers Cu(I) to the cytoplasmic enzyme copper-zinc superoxide dismutase (SOD) (left). Coxl7 shuttles Cu(I) to cytochrome c oxidase (CCO) in the mitochondria (bottom). Mitochondrial proteins Scol and Sco2 may also play a role in copper delivery to the CuA and CuB sites of CCO. Copper metabolism and iron metabolism are linked through the actions of Fet3, a copper-containing ferroxidase required to bring iron into the cell (lower right) (see text).

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