The Effects of γ-radiolysis on Solutions of Papain

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Abstract
Highly-purified papain was irradiated in atmospheres of oxygen, nitrogen and nitrous oxide. A simultaneous decline in papain activity and in the sulphydryl content was observed. By use of dithiothreitol the loss of enzymatic ability was separated into recoverable and non-recoverable parts. Amino acid analyses demonstrated that some non-recoverable damage consisted of oxidation of cysteine residues to cysteic acid. The remainder was by formation of products which, on hydrolysis in two different acids, yielded analyses indistinguishable from those for unirradiated enzyme. These products may include sulphenic acid and the results of disulphide interchanges incorporating the essential Cys 25. Similar but readily reducible products must account for the recoverable damage observed on radiolysis.