N-terminal Glycation of Proteins and Peptides in Foods andin Vivo
Specific determination of N-(2-furoylmethyl)valine (FM-Val) together with furosine in acid hydrolyzates of human hemoglobin of healthy volunteers (n=6) and diabetic patients (n=14) by means of reversed-phase HPLC with electrospray ionizationtime-of-flight mass spectroscopy is reported. Whereas FM-Val is formed during acid hydrolysis of the N-terminal hemoglobin adduct N-fructosylvaline, furosine results from acid degradation of lysine residues glycated at the ?-amino group. Quantification was based on the use of synthesized isotopomers, namely N-[2-(13C6)furoylmethyl]valine and N-?-[2-(13C6)furoylmethyl]lysine, thus enabling interference-free detection and calibration. Taking the conversion factors into account, the amount of N-terminally bound N-fructosylvaline in human hemoglobin was between 518 and 774pmol/mg protein for healthy volunteers and between 586 and 1426pmol/mg protein for diabetic patients. Derivatization at the side chain of peptide-bound lysine residues to N-?-fructosyllysine was from 1156 to 1753pmol/mg protein for healthy controls and from 1191 to 2409pmol/mg protein for diabetics. For these patients, the amount of N-fructosylvaline showed good correlation with the values for HbA1c. The significantly higher relative extent of glycation at the N terminus compared to side-chain glycation points to a specific and intraindividual capacity for enzymatic deglycation in human erythrocytes, which can be assessed using the proposed method.
glycation furosine diabetes n-fructosylvaline amadori compounds hemoglobin hba1c