An on-column derivatization method for the determination of homocysteine-thiolactone and protein N-linked homocysteine.

Homocysteine (Hcy) is incorporated into protein via a reaction of the thioester Hcy-thiolactone with ε-amino group of a protein lysine residue generating N-Hcy-protein. This reaction impairs and alters protein's function and has been implicated in atherothrombotic disease. Here, we describe new high-performance liquid chromatography assays for the determination of Hcy-thiolactone, protein N-linked Hcy, and Hcy based on an on-column derivatization with o-phthaldialdehyde and fluorescence detection. The on-column derivatization generates narrow peaks, which allows fast run times (3-5 min) and facilitates determination of N-linked Hcy directly from acid hydrolysates of plasma protein. Utility of these assays was demonstrated with human urine and plasma samples.