Inactivation of plasma α₁-proteinase inhibitor by acrolein: Adduct formation with lysine and histidine residues

Four new peaks were observed upon amino acid analysis of α₁-proteinase inhibitor (α₁-PI), which was inactivated by acrolein under in vitro conditions. The first peak emerged just before ammonia, the second and third between ammonia and lysine, and the fourth between histidine and arginine. The new fourth peak was also observed when model compounds of lysine (N-acetyllysine or polylysine) were reacted with acrolein and subsequently processed for amino acid analysis. This new compound was purified by high-voltage paper electrophoresis and subjected to fast atom bombardment mass spectrometry, which showed a protonated molecule ion at m/z 203 [M + H]⁺ followed by m/z 186 [M + H⁺ - NH₃]⁺. This compound was thus identified as 3-oxopropyllysine, a lysine adduct of acrolein. Similarly, when a model polypeptide of histidine, polyhistidine, was reacted with acrolein under the same conditions as α₁-PI, three new peaks (besides histidine) emerged from the column. Their elution times corresponded to the first three new peaks found in the hydrolysates of acrolein treated α₁-PI.