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 398nm (excitation maximum) and 470nm (emission maximum). The amount of the fluorescent residues was estimated to be less than 0.2% of the ε-amino groups. Most of the malonaldehyde was incorporated into the ε-amino groups as nonfluorescent aminopropenal residues (22%) which exhibited an absorption maximum at 280nm and were reactive to 2-thiobarbituric acid. These residues are unstable and might produce cross-links by reacting with unmodified ε-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 340-360nm and emission maxima at 410-430nm. Studies of the characteristics of fluorescence of these modified polylysines revealed that the fluorophore in the hydroperoxide-modified polylysine was distinguishable from that of the malonaldehydemodified polylysine. It is likely that the fluorophores and cross-links in the hydroperoxide-and the monofunctional aldehyde-modified polylysines were formed by different mechanisms from those involved in the case of malonaldehyde.