Patent ID: 8435757

Claim:
A method for determining activity of at least one endopeptidase in a body fluid comprising: (a) adding to the body fluid a dose of at least one reporter substrate, the molecules of which include a peptide having a cleavage motif of the at least one endopeptidase and that has a cleavage site with a first anchor located on one side of the cleavage site and a second anchor that differs from the first anchor located on another side of the cleavage site; (b) incubating the fluid resulting from step (a) for a predetermined time under predetermined conditions, so that added reporter substrate molecules are subjected to enzymatic activity of endopeptidases and exopeptidases contained in the body fluid; (c) extracting all molecules carrying one of the two anchors so that all reporter substrate molecules not cleaved are extracted; (d) extracting any remaining reaction products using the anchor not used in step (c); and (e) measuring the reaction products extracted in step (d) by mass spectrometry to determine the quantity thereof, which in relation to an amount of reporter substrate molecules in the dose used in step (a) represents activity of the at least one endopeptidase.