An ESR study of radiation effects in metalloproteins.

Glassy methanolic and ethanolic solutions of molecular oxygen were exposed to X-rays at 4.2 K. A marked inhibition of the formation of e-t centres together with formation of O2- was observed. The results suggest that the environment of O2 in methanol is such that initial hydrogen-bond transfer to O2- is facile even at 4.2 K. In ethanol, O2- is too far from hydrogen bonded OH groups for this mechanism to operate. Dilute aqueous glassy solutions of the enzyme superoxide dismutase (SOD) were exposed to ?-radiation. Reduction of the native Cu(II) centre to Cu(I) was observed. A reaction was established between this reduced form and O2-. Potassium hexacyanoferrate II was shown to be a suitable chemical reducing agent for SOD after purification, whereas sodium dithionite was shown to modify the copper centre. Study of the disulphide bridge of reduced SCD revealed RSSR- radicals and, in sane cases, species 'X', depending on the nature of the reducing agent. The pH dependence of S(X) and the effect of some anions has been illustrated and serves to confirm documented results. Dilute aqueous glassy solutions of powered haemoglobin and diluted sarrples of whole blood were exposed to ?-radiation. ? and ? subunit haem Fe-O2 centres were identified at 77 K and several spectral changes recorded during warming. Tentative identification of these species has been made.