MODIFICATION OF LYSINE AMINO-GROUPS BY THE LIPID-PEROXIDATION PRODUCT4,5(E)-EPOXY-2(E)-HEPTENAL

The reaction between 4,5(E)-epoxy-2(E)-heptenal (EH) and L-lysine was studied to characterize some of the compounds that may be produced whe n proteins react with peroxidizing lipids. A mixture of EH and lysine was incubated overnight at room temperature and then fractionated by h igh-performance liquid chromatography (HPLC). Fractions were freeze-dr ied and characterized by H-1 and C-13 nuclear magnetic resonance (NMR) and mass spectrometry. Four major pyrrole derivatives were obtained, namely 1-(5'-amino-1'-carboxypentyl)pyrrole (3), ino-1'-carboxypentyl) -2-(1''-hydroxypropyl)pyrrole (diastereomers 5 and 8), 1-(5'-amino-5'c arboxypentyl)pyrrole (7), and ino-5'-carboxypentyl)-2-(1''-hydroxyprop yl)pyrrole (9). In addition, several lysine complexes were detected. A polymer (Ib) that was responsible for the color and the fluorescence produced in the reaction was isolated by gel filtration chromatography from a fraction obtained by HPLC. Formation of pairs of analogs (5 an d 3, 9 and 7) with and without a substituent in position 2 of the pyrr ole ring suggested that the compounds were produced by the same mechan ism, with the formation of the S-unsubstituted pyrroles corresponding to the loss of the g-substituent as propanal; propanal was detected by headspace capillary gas chromatography. A reaction mechanism is propo sed based on the NMR data obtained when the reaction was monitored in real time in an NMR tube. The results suggest that pyrrolic amino acid s 7 and 9 may be present in proteins that have been damaged by peroxid izing lipids.