Radiation Chemical Studies of Hemocyanin in Oxygen-Free Media

Abstract

The oxygen-carrying capacity of Busycon and Limulus hemocyanins is eliminated following irradiation of the protein with cobalt-60 γ-rays in neutral, oxygen-free media. The loss of oxygen-carrying capacity of the protein is measured from the change of the characteristic copper band at 340 nm, before and after irradiation. The limiting ${\rm G}(-{\rm O}_{2})$ values in the absence of scavengers are 0.026 and 0.044 for Busycon and Limulus hemocyanins, respectively. Radiation effects in oxygen-free media on Busycon and Limulus hemocyanins can either be enhanced or prevented by appropriate scavengers. The Busycon methemocyanin activity is restored by the hydrated electron, $e_{{\rm aq}}^{-}$, and the secondary ${\rm CO}_{2}{}^{-}$ radical. The loss of oxygen-carrying capacity of hemocyanin by γ irradiation is attributed, therefore, to the OH radical which oxidizes the protein-bound copper at the active site, thus forming methemocyanin. The restoration of the oxygen-carrying capacity of Busycon methemocyanin is...