Free radical polymerization and lipid binding of lysozyme reacted with peroxidizing linoleic acid

Insolubilization and polymerization of proteins exposed to peroxidizing lipids may be due either to cross-linking with incorporation of fragments of the lipid oxidation products, or to free radical transfer from lipid to protein and subsequent free radical polymerization of protein. The second mechanism which has been proposed was inferred from measurements of electron spin resonance signals in proteins. In this study, uniformly labeled linoleic acid, ¹⁴C(U)] LA, was reacted with lysozyme. Volatile oxidation products of LA were also used in some experiments. Incubation was done in the absence of water. Oligomers of lysozyme, as well as the monomer, were isolated after incubation, and the ¹⁴C] label incorporated into each fraction was determined. The results show that the dominant mechanism of protein polymerization after exposure to peroxidizing linoleic acid is the transfer of free radical from lipid to protein, and subsequent free radical polymerization.