| abstract |
A polypeptide reactive reagent having the formula PRG-Z wherein 'PRG' is a polypeptide reactive group which optionally binds to a capture reagent, and wherein 'Z' is an aryl, substituted aryl, alkyl, substituted alkyl, lower alkyl or substituted lower alkyl group in which one or more atoms can be differentially labeled with one or more stable isotopes 'X', wherein 'X' is selected from the group consisting of H and D, is described. |