The early glycation products of the Maillard reaction: mass spectrometric characterization of novel imidazolidinones derived from an opioid pentapeptide and glucose.
Glucose-substituted imidazolidinones related to the endogenous opioid peptide leucine-enkephalin have been investigated using fast atom bombardment tandem mass spectrometry (FAB-MS/MS) and electrospray ionization tandem mass spectrometry (ESI-MS/MS). In addition to Amadori compounds, the studied imidazolidinones represent a novel type of the early glycation products formed in the Maillard reaction. To obtain insight into the fragmentation behavior of these carbohydrate-peptide adducts, we also studied synthetic precursors of the glucose-substituted imidazolidinones as well as the corresponding isopropylidene derivatives. The collision-induced dissociation (CID) spectra of [M + H](+) ions of all these imidazolidinones have been compared. Detailed analysis showed that fragmentation of each compound generates two ions at m/z 566 and m/z 598 which are characteristic and undoubtedly confirm the imidazolidinone-type structure. These two significant ions were identified as the M + 10 and M + 42 modifications of the N-terminus of the parent opioid pentapeptide effected by the carbohydrate moiety. Furthermore, the ion at m/z 178 is identified as the M + 42 modification of the immonium ion of the N-terminal amino acid (tyrosine) also effected by the carbohydrate moiety. They can be used as diagnostic ions for imidazolidinone-type compounds in studying the Maillard reaction. Thus, we have demonstrated the utility of FAB-MS/MS and ESI-MS/MS in the structural determination and identification of such novel peptide-carbohydrate adducts, useful in understanding the details of the mechanism of non-enzymatic glycation in vivo.
Roscić
M
M
Department of Organic Chemistry and Biochemistry, Ruder Bosković Institute, PO Box 180, 10002 Zagreb, Croatia. roscic@rudjer.irb.hr
Versluis
C
C
Kleinnijenhuis
A J
AJ
Horvat
S
S
Heck
A J
AJ
D000475:Alkenes / Q000032:analysis; D005947:Glucose / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D015416:Maillard Reaction; D018847:Opioid Peptides / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D016339:Spectrometry, Mass, Fast Atom Bombardment / Q000379:methods*
D000475:Alkenes; D007093:Imidazoles; D018847:Opioid Peptides; C013658:propylene; D005947:Glucose