Immunological relevance of malonic dialdehyde. I. Preparation of Schiff's bases from lysozyme or polylysine reacted with malonic dialdehyde.

Malonic dialdehyde (MDA) is produced in all mammalian tissues either as an end product of lipid peroxidation or as a by-product of arachidonic acid metabolism. It may either be quickly oxidized to carbon dioxide or combine covalently with primary amino groups of proteins, phospholipids or nucleic acids. In the latter case, fluorescent Schiff's bases with 1-amino-3-iminopropene (AIP) bridges are produced. MDA metabolism is now fairly well elucidated, while that of MDA-cross-linked biological molecules remains unknown. Aiming at investigating the fate of such cross-linked molecules in mammalian organisms, and their biological relevance, we tried in the present study to prepare reproducibly Schiff's bases from chicken egg white lysozyme reacted with MDA. The resulting mixture of different Schiff's bases (ML) was fractionated into single oligomeric fractions by gel-filtration chromatography. ML and the single oligomeric fractions obtained from this mixture were controlled by fluorescence measurements for their content of AIP bridges, and by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE) for their content of different oligomers. ML contained monomers, dimers, trimers and other oligomers, as shown by SDS-PAGE. The corresponding single oligomeric fractions were satisfactorily separated by gel-filtration chromatography (purity better than 94%, as determined by SDS-PAGE). Schiff's bases from poly-L-lysine reacted with MDA (MP) were also prepared. Their fluorescence emission spectrum was similar to that of ML and to that of the single oligomeric fractions obtained from ML.