Interaction of Radiation-generated Radicals with Myoglobin in Aqueous Solution

Summary

The γ-radiolysis of aqueous solutions of ferrimyoglobin in the presence of N₂O at pH 7·3 has been examined as a function of added catalase and oxygen. Changes in the nature of the heme group have been monitored by visible absorption spectrophotometry and analysed quantitatively by a multiple wavelength method based on Beer's Law. Simple chemical analyses have been used to confirm qualitative identification of the product derivatives. As observed previously, the ferriheme is reduced by indirect globin-mediated action initiated by ·OH/H·. The yield of reduced product decreases as [O₂] increases. Conversion to ferrylmyoglobin through the participation of H₂O₂ derived from irradiated water and from protein-mediated processes in oxygenated solution, is eliminated by the presence of catalase. Formation of a hemichrome form of ferrimyoglobin is apparent at higher doses in the presence of O₂. These results demonstrate that oxygen plays an important role in controlling the nature and extent of redox that manifests ultimately on the heme group of ferrimyoglobin as a result of the initial interaction of ·OH/H·.

• ferrimyoglobin
• ferrylmyoglobin
• hemichrome
• hydroxyl radi-cals
• activated oxygen