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Evidence that malondialdehyde-derived aminoenimine is not a fluorescent age pigment

K Itakura1, K Uchida

  • 1Faculty of Education, Aichi University of Education, Kariya 448-8542, Japan. kitakura@auecc.aichi-edu.ac.jp

Chemical Research in Toxicology
|May 23, 2001
PubMed

Insights

Malondialdehyde (MDA) modification of proteins is linked to lipofuscin fluorescence. This study isolated and confirmed that the proposed aminoenimine structure from MDA and lysine is nonfluorescent, refuting its role in lipofuscin fluorescence.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Aging Research

Background:

  • Lipofuscin, a cellular pigment associated with aging, is thought to accumulate due to protein modifications.
  • Malondialdehyde (MDA), a product of lipid peroxidation, has been implicated in forming fluorescent compounds within lipofuscin.
  • A proposed fluorophore structure involves an aminoenimine formed from MDA and lysine residues, but its fluorescence has been debated due to lack of isolation.

Purpose of the Study:

  • To investigate the role of aminoenimine structures in lipofuscin fluorescence.
  • To isolate and characterize the aminoenimine formed from MDA and lysine.
  • To determine if this isolated aminoenimine exhibits fluorescence.

Main Methods:

  • Reaction of malondialdehyde (MDA) with a lysine derivative (N(alpha)-tert-butoxycarbonyl-L-lysine, Boc-Lys) under neutral pH conditions.
  • Isolation and purification of the resulting aminoenimine product, N,N'-bis[5-(tert-butoxycarboxamido)-5-carboxypentyl]-1-amino-3-iminopropene [(Boc-Lys)(2)MDA].
  • Spectroscopic analysis to confirm the structure and measure the fluorescence of the purified compound.

Main Results:

  • Successfully isolated the aminoenimine, (Boc-Lys)(2)MDA, formed from MDA and Boc-Lys.
  • The purified (Boc-Lys)(2)MDA exhibited no detectable fluorescence.
  • This provides the first conclusive evidence regarding the fluorescence properties of this specific aminoenimine structure.

Conclusions:

  • Aminoenimine structures formed from malondialdehyde and lysine residues do not contribute to the fluorescence of lipofuscin.
  • The proposed aminoenimine pathway is not responsible for lipofuscin autofluorescence.
  • This finding clarifies a long-standing question in aging and oxidative stress research.

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