title: Time-resolved europium fluorescence in enzyme activity measurements: a sensitive protease assay.
abstract: A method for incorporating into proteins a nonradioactive Eu3+ label, which exhibits fluorescence of a long decay time in the presence of suitable ligands, is described. As an example of the use of this label the method has been developed to work as a sensitive protease assay. By hydrolyzing the Eu3+-labeled casein, bound to an insoluble matrix (Sepharose 4B or Affi-Gel 10), with proteases and measuring the Eu3+ released with a pulsed time-resolved fluorometer it was possible to detect as low as 2.5, 1.0, or 1.0 ng of alpha-chymotrypsin, trypsin, or subtilisin, respectively.
mesh_terms: D000818:Animals; D001407:Bacillus / Q000201:enzymology; D002417:Cattle; D002918:Chymotrypsin / Q000378:metabolism*; D005063:Europium; D007700:Kinetics; D008832:Microchemistry; D010179:Pancreas / Q000201:enzymology; D013050:Spectrometry, Fluorescence / Q000379:methods; D013381:Subtilisins / Q000378:metabolism*; D013552:Swine; D014357:Trypsin / Q000378:metabolism*
chemical_list: D005063:Europium; D013381:Subtilisins; D002918:Chymotrypsin; D014357:Trypsin