Polylysines modified with malonaldehyde, hydroperoxylinoleic acid and monofunctional aldehydes

The interaction of components of peroxidized lipids with polylysine, as a model of protein, was investigated by evaluating the fluorescence and cross-links produced. Treatment of polylysine with 1/3 molar excess malonaldehyde at pH 7.5 gave modified polylysines containing 1,4-dihydropyridine-3,5-dicarbaldehyde residues that fluoresced at 398 nm (excitation maximum) and 470 nm (emission maximum). The amount of the fluorescent residues was estimated to be less than 0.2% of the epsilon -amino groups. Most of the malonaldehyde was incorporated into the epsilon -amino groups as non-fluorescent aminopropenal residues (22%) which exhibited an absorption maximum at 280 nm and were reactive to 2-thiobarbituric acid. These residues are unstable and might produce cross-links by reacting with unmodified epsilon -amino groups. Reaction of polylysine with hydroperoxylinoleic acid, acetaldehyde or n-hexylaldehyde produced cross-linked polylysines which exhibited much weaker fluorescence with excitation maxima at 340-360 nm and emission maxima at 410-430 nm.