Radiation-induced Aggregation of Bovine Pancreatic Ribonuclease

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Abstract
Purified bovine pancreatic ribonuclease in aqueous solution at a concentration of 10 mg per millilitre aggregated when exposed to 60Co gammaradiation. Aggregation was demonstrated by Sephadex chromatography. The aggregation process was inhibited by oxygen and by chemical protective agents. In the presence of oxygen, partially oxidized, partially-active ribonuclease was formed during irradiation. In the absence of oxygen, aggregated, enzymically-inactive protein was produced. 3,3′-guanidinopropyl disulphide (GPD) completely inhibited the aggregation process. Aggregation of irradiated ribonuclease was observed in solutions of ph 1 to 8. Irradiation of lyophilized, dry ribonuclease failed to produce aggregate. Fragmentation products from irradiated protein were not observed with Sephadex G-25 chromatography. Performic-acid-oxidized ribonuclease also formed aggregates upon irradiation. Total amino-acid analysis of the aggregate indicated that one lysine residue of the enzyme was chemically altered in the aggregate. A mechanism for radiation protection by chemicals based upon the ability of these chemicals to terminate the aggregation process is suggested.

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