X-ray absorption study of Cu, Zn SOD under high pressure

We have investigated Cu,Zn Superoxide Dismutase (Cu,Zn SOD) metal sites at high pressure using X-ray absorption. XAS (X-ray Absorption Spectroscopy) g ives information on local structure and it is particularly suited to metal site investigation. To the best of our knowledge, this is the first time th at protein conformational states have been investigated using the high pres sure XAS technique. Cu, Zn SOD catalyses the dismutation of toxic ox)gen ra dicals produced in cells; this reaction occurs at the copper metal site. St ructural changes around the copper, induced by pressure, can be directly re lated to protein substates. Their characterisation is thus important in the understanding of protein activity. The high-pressure device was a Paris-Edinburgh large volume cell. Experiments were performed on lyophilised Cu, Zn SOD between 0 and 48 kbar at the copper and zinc K-edges. The two metal local atomic environments hav e a different behaviour as pressure increases: copper exhibits a more flexi ble environment; on the contrary, zinc shows small structural modifications . We have identified a state, formed between 3 and 8 kbar, which is stable up to 48 kbar.