Structural Characterisation of Acetaldehyde Adducts Formed by a Synthetic Peptide Mimicking the N‐Terminus of the Hemoglobin β‐Chain Under Reducing and Nonreducing Conditions

Abstract

This work was carried out to elucidate the structures resulting from acetaldehyde-induced modifications at the haemoglobin P-chain N-terminal residues under different experimental conditions. A synthetic peptide (Val-His-Leu-Thr-Pro-Glu-Cys) of d z 798, which represents the six N-terminal residues of the haemoglobin P-chain N-terminus with an additional C-terminal cysteine, was used as a model compound. Peptide-acetaldehyde adducts were separated by reverse-phase HPLC. Fast-atom-bombardment MS and linked-scan (BE) spectra were used to study adduct structures. Under nonreducing conditions at pH 7.4 (1 : 10 peptide/acetaldehyde molar ratio), two types of adducts of m/z 824 were formed, both with modifications at the N-terminal valine. These two adducts were shown to be a Schiff base, and a cyclic 2-methyl-imidazolidine-4-one. The 2-methyl-imidazolidine-4-one adduct was demonstrated to be formed via the Schiff base and to undergo dissociation gradually after 24 h. Reducing conditions at pH 7.4 (peptidelacetaldehyde molar ratio of 1 : 1 with 20 mM NaCNBH,) resulted in the formation of an adduct of d z 826. which was shown to be an N-ethylated adduct of valine. A small amount of nonreduced adducts were also formed under these conditions. Reducing conditions at pH 9.0 (1 : 10 peptidebacetaldehyde molar ratio with 20 mM NaCNBH,) yielded two secondary, i.e. diethylated ( d z 854), products very rapidly.The cysteine residue of the peptide was not found to form an adduct with acetaldehyde under physiological pH.

Acute and Long-Term Stability Studies of Deoxy Hemoglobin and Characterization of Ascorbate-Induced Modifications

“…Imidazolidinone structures have been postulated to form at the N-terminus of the globin in reactions of human hemoglobin A 0 with aldehydes. [39][40][41][42] Our results also indicate that the modification is likely to contain labile carboxy and hydroxy groups, which is consistent with the observed neutral loss of 44Da-and 18 Da-derived fragments. The proposed structure for the modification is presented in Figure 15.…”

Characterization of N‐terminal formaldehyde adducts to hemoglobin

“…The literature has reported that reaction of hemoglobin with acetaldehyde can result in two types of adducts of the same mass, one being a Schiff base (imine) and the other a 2-methyl-imidazolidin-4-one. [31] FA is expected to react similarly. Sodium borohydride can efficiently reduce imines into secondary or tertiary amines.…”

“…The formation of an imidazolidone structure from FA-N-terminal peptide adducts of hemoglobin agrees with findings from other researchers on reactions of insulin with FA [38] and of hemoglobin with acetaldehyde. [31] This study is the first report of the imidazolidone structure for FA and these peptides.…”

“…[23,24] The reaction products of hemoglobin with sugars and certain aldehydes have been studied, [15,[25][26][27][28][29][30] and the structures of adducts such as Schiff bases and imidazolidinones are described in the literature. [31][32][33] However, little is known about the reaction products of FA at the N-terminus of hemoglobin. [29,34] In this study, we investigated the N-terminal, FA adducts by using VHLTPEEK and VLSPADK as model peptides.…”

Rapid complexing of oxoacylglycerols with amino acids peptides and aminophospholipids

“…A glycerophosphoethanolamine-malonaldehyde-glycerophosphoserine Schiff base conjugate was identified in rabbit lens oxidized in vitro, and similar reactions are believed to occur in human cataract (8). Schiff base formation between peptide-mimicking the hemoglobin β-chain Nterminus and acetaldehyde has been reported (9). Acetaldehyde is the major oxidation product of ethanol in vivo, and its adducts with hemoglobin can serve as markers of ethanol intake (10).…”