Di-iron carboxylate proteins perform a wide range of chemical reactions in the cell. These reactions often involve activation of dioxygen to generate highly oxidative species that can be used in catalysis. One member of the di-iron carboxylate family is the enzyme ribonucleotide reductase (RNR). This enzyme is essential for DNA synthesis since it is a key enzyme on the pathway for de-novo synthesis of deoxyribonucleotides, the building blocks of DNA. To perform its catalytic function RNR is dependent on a protein radical. In this thesis I have used x-ray crystallographic methods to investigate the mechanism of O₂ activation and radical generation in the R2 subunit of RNR. These structural studies have lead to a proposal of a detailed mechanism, which could be common to most O₂ activating di-iron carboxylate proteins. The alternative oxidase is a membrane protein that has been proposed to belong to the di-iron carboxylate family. This protein is a ubiquinol/oxygen oxidoreductase and can act as a terminal electron acceptor in the respiratory chain. I have used homology modelling to make a structural model of this enzyme, which provides new insights into its functions and its relationship to the other di-iron carboxylate proteins.

Given the strong oxidative power of the di-iron carboxylate proteins they would be very useful as oxidants in various industrial applications. Another part of my project has been aimed towards the design of a di-iron carboxylate enzyme tailored for industrial and environmental applications using a small and stable di-iron carboxylate protein as a starting framework, namely the bacterioferritin protein. This work has lead to the synthesis of a gene library with many potential enzymatic activities.