Reduction of lipid hydroperoxides by apolipoprotein B-100

We have previously isolated two proteins which can reduce phosphatidylcholi ne hydroperoxide (PC-OOH) from human blood plasma and identified one of the proteins as apolipoprotein A-I (Mashima, R., et al. (1998) J. Lipid Res. 3 9, 1133-1140), In the present study we have identified the other protein as apolipoprotein B-100 (apo B-100) by amino acid sequence analysis of its tr yptic peptides. The reactivity of lipid hydroperoxides with apo B-100 decre ased in the order of PC-OOH > linoleic acid hydroperoxide > cholesteryl est er hydroperoxide under our experimental conditions. Pretreatment of apo B-1 00 with chloramine T, an oxidant of methionine, diminished the PC-OOH-reduc ing activity, indicating that some of 78 methionines are responsible for th e reduction of PC-OOH. Despite the presence of 6 methionines in albumin, al bumin was inactive to reduce PC-OOH. Free methionine was also inactive. The se data suggest that the accessibility and binding of lipid hydroperoxides to the protein methionine residues are crucial for reduction of lipid hydro peroxides. (C) 1999 Academic Press.