Activities of the oligomeric enzymes urease and l-glutamate dehydrogenase were measured after exposure as dry preparations to various doses of electron radiation. Inactivation curves were exponential. ‘Target sizes’ deduced from these were small compared with the molecular weights of the whole enzyme molecules, but accorded well with independent estimates of the sizes of functional subunits. It was concluded that, when these were in associated from, there could be no transfer of absorbed energy between subunits.

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