Tritium labelling of ribonuclease by the gas‐exposure method, as improved by an electric discharge

When lyophilized samples of bovine pancreatic ribonuclease are exposed to tritium gas, the exchange process can be markedly improved by applying high frequency electric discharges. Labelling has been carried out for 5, 15 or 30 minutes periods. Labile radioactivity, was then removed by means of molecular sieving and repeated lyophilizations, the tritiated protein being submitted to further purification by ion-exchange chromatography. The specific radioactivity of such purified samples is in the Curie/mmole range, and the biological activity of the enzyme remains well preserved. The distribution of tritium atoms among component aminoacids has been determined, after acid hydrolysis of the labelled protein.