Chemical and Biological Alterations Induced by Irradiation of I131 Labeled Human Serum Albumin

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Abstract
Human serum albumin labeled with I131 was irradiated at protein concentrations of 20 [mu]g/ml to 50 mg/ml with X-rays at dosage levels of 45 to 135 kilorad and with iodide131 at a dosage level of 84 kilorad. Biologic alteration induced by irradiation was evidenced by susceptibility to rapid metabolic degradation in vivo. This alteration was detectable with protein concentrations of 5 mg/ml or less and irradiation dosages corresponding to those received in one week by solutions initially containing 0.8 mc I131/ml or greater. Following irradiation, reactive sulfhydryl groups were demonstrated by reduction of ferricyanide in the absence but not in the presence of p-chloromercuribenzoate. Anomalous migration of I131 labeled frag-ments on paper electrophoresis and liberation of I131 as iodide were also observed. The extent of alteration induced was a direct function of the radiation dose and was inversely related to the protein concen-tration during irradiation. The potential radiation damage to I131 labeled proteins of high specific activity is discussed and a method for protection agajnst radiation damage is suggested.