Changes in the conformation of apoliprotein B-100 in the early stages of copper-mediated low density lipoprotein oxidation have been monitored by infrared spectroscopy. During the lag phase no variation in structure is observed, indicating that copper binding to the protein does not significantly affect its structure. In the propagation phase, while hydroperoxides are formed but the protein is not modified, no changes in secondary structure are observed, but the thermal profile of the band corresponding to α-helix is displaced in frequency, indicating changes in tertiary structure associated with this conformation but not with β-sheet components. When aldehyde formation starts, a decrease of ~3% in the area of bands corresponding to α-helix and β-sheet is produced, concomitantly with an increase in β-turns and unordered structure. The two bands corresponding to β-turns vary as well under these conditions, indicating changes in these structures. Also at this stage the thermal profile shows variations in frequency for the bands corresponding to both α-helix and β-sheet.The results are consistent with the hypothesis that as soon as the polyunsaturated fatty acids from the particle core are modified, this change is reflected at the surface, in the α -helical components contacting the monolayer.
