N-terminal Gly cation of Proteins and Peptides in Foods and in Vivo

摘要

Specific determination of 7V-(2-furoylmethyl)valine (FM-Val) together with furosine in acid hydrolyzates of human hemoglobin of healthy volunteers (ra = 6) and diabetic patients (n= 14) by means of r eversed-phase HPLC with electrospr ay ionization-time-of-flight mass spectroscopy is reported. Whereas FM-Val is formed during acid hydrolysis of the N-terminal hemoglobin adduct Af-fructosylvaline, furosine results from acid degradation of lysine residues glycated at the e-amino group. Quantification was based on the use of synthesized isotopomer s, namely iV-[2-(13C6)furoylmethyi]vaIine and 7V-?-[2-(13C6)furoylmethyl]lysine, thus enabling interference-free detection and calibration. Taking the conversion factors into account, the amount of N-ter minally bound A^-fructosylvaline in human hemoglobin was between 518 and 774 pmol/mg protein for healthy volunteers and between 586 and 1426 pmol/mg protein for diabetic patients. Derivatization at the side chain of peptide-bound lysine residues to iV-e-fructosyllysine was from 1156 to 1753 pmol/mg protein for healthy controls and from 1191 to 2409 pmol/mg protein for diabetics. For these patients, the amount of iV-fructosylvaline showed good correlation with the values for HbAic. 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.