Cytotoxic action of membrane lipid peroxidation product 4-hydroxynonenal (HNE) is due mainly to its facile reactivity with proteins (Esterbauer, H., Schaur, R. J., and Zollner, H. (1991) Free Radical Biol. Med. 11, 77-80). In the present study, the detailed mechanism of HNE modification of a key enzyme in intermediary metabolism, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), is studied mainly focusing on the formation of HNE-amino acid adducts in the enzyme. When GAPDH (1 mg/ml) was treated with 0-2 mM HNE in sodium phosphate buffer (pH 7.2) for 2 h at 37 degrees C, the enzyme was inactivated by HNE in a concentration-dependent manner. The loss of enzyme activity was associated with the loss of free sulfhydryl groups. Following its reduction with NaBH4, amino acid analysis of the HNE-modified enzyme demonstrated that histidine and lysine residues were also modified. At concentrations lower than 0.5 mM, HNE reacts preferentially with cysteine and lysine residues. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the HNE-modified enzyme suggested the formation of intra- and intermolecular cross-links of the enzyme subunit. The HNE-dependent loss of amino acid residues was accompanied by the generation of protein-linked carbonyl derivatives as assessed by reduction with NaB[3H]H4 and reaction with 2,4-dinitrophenylhydrazine. Thus, the conjugation of all the amino acids appears to involve Michael addition type reactions in which the carbonyl function of HNE would be preserved. The modified histidine residues were quantitatively recovered as the HNE-histidine adduct. However, only 28% of the missing lysine could be accounted for as the HNE-lysine derivative, and only 15.6% of the modified cysteine could be accounted for as the HNE-cysteine thioether derivative. It is proposed that the carbonyl groups of the HNE-derived Michael addition products may undergo secondary reactions with the amino acid groups of lysine residues to yield inter- and intrasubunit cross-links.