The end product of transglutaminase crosslinking: Simultaneous quantitation of [Nε-(γ-glutamyl) lysine] and lysine by HPLC-MS3

Transglutaminases catalyze the formation of N-epsilon-(gamma-glutamyl) isodipeptide crosslinks between proreins. These enzymes are thought to participate in a number of diseases, including neurological disease and cancer. A method associating liquid chromatography and multiple stage mass spectrometry has been developed for the simultaneous quantitation of [N-epsilon-(gamma-glutamyl) lysine] isodipeptide and lysine on an ion trap mass spectrometer. Highly specific detection his been achieved in MS3 mode, The method includes a derivatization step consisting of butylation of carboxylic groups and acetylation of amide groups, a liquid-liquid extraction and, a 19-min separation on a 100 x 2.1-mn Beta-basic C-18 column with air acetonitrile gradient elution. C-13(6)-N-15(2) isotopes of the isodipeptide and the lysine serve as internal standards. The assay was linear in the range of 50 pmol/ml to 75 nmol/ml for the isodipeptide and the range of 10 nmol/ml to 3.5 mu mol/ml for the lysine, with correlation coefficients greater than 0.99 for both ions. Intra- and inter-day coefficients of variation ranged from 3.5 to 15.9%. The Method Was successfully applied to human biological samples known to be crosslinked by transglutaminase such as cornified envelopes of epidermis, fibrin, and normal and Huntington disease brain. (C) 2008 Elsevier Inc. All rights reserved