Casein labelled with Iodine-131 as a Substrate for the Measurement of Trypsin and Chymotrypsin

Abstract

THE spectrophotometrie method of Kunitz¹is a marked improvement over previous methods for the measurement of trypsin and chymotrypsin activity. This procedure involves a measurement of the optical density at 280 mµ. of the trichloracetic acid-soluble products formed during the enzyme hydrolysis of casein; it becomes impractical, however, where large concentrations of 280 mµ absorbing materials are present, such as in sera. In this communication, a modification of this procedure will be described which utilizes casein labelled with iodine-131 as the substrate and the measurement of radioactivity as an estimate of enzyme activity.