STABLE ACETALDEHYDE ADDUCTS - STRUCTURAL CHARACTERIZATION OF ACETALDEHYDE ADDUCTS OF HUMAN HEMOGLOBIN N-TERMINAL BETA-GLOBIN CHAIN PEPTIDES

Acetaldehyde is the first oxidation product of ethanol in vivo. Our ea rlier work showed that with sufficient acetaldehyde, five of the six p ossible sites of the peptide pentalysine were modified as a Schiff bas e (Braun KP, et al: J Biol Chem 270:11263-11266, 1995). However, we we re unable to deduce unequivocally which site was unmodified. Lysine re sidues, as well as the amine terminal valine residues, in hemoglobin h ave been implicated as target structures for acetaldehyde adducts resu lting from ethanol consumption. Hemoglobin adducts of acetaldehyde hav e been used clinically as a marker of ethanol consumption, but the che mical nature of these adducts remains undefined. As part of our contin uing structural characterization of acetaldehyde-protein adduct format ion, we studied the peptides Val-His-Leu-Thr-Pro and Val-His-Leu-Thr-P ro-Val-Glu-Lys, from the amine terminus of the beta-globin chain of he moglobin, in vitro. Both peptides have at least one potential site for adduct formation. In the octapeptide, the N-terminal amine group of V al as well as the epsilon-amine group of the lysine sidechain can pote ntially be modified by acetaldehyde. We used mass spectrometry, carbon -13 nuclear magnetic resonance, and Raman spectroscopy and characteriz ed stable Schiff base acetaldehyde adducts of these two peptides at bo th reactive sites. The identification of stable Schiff base adducts wi th the N-terminal peptides of the beta-chain of hemoglobin as well as with epsilon-amino groups of lysine provides another possible means of monitoring ethanol consumption. The functional implications of these stable Schiff bases remains undefined.