Distribution Of Hydroperoxides Research Articles

Susceptibility to peroxidation of the major mycelial lipids of Cunninghamella echinulata

AbstractThe distribution of hydroperoxides among lipid fractions (namely neutral lipids, glycolipids, sphingolipids, and phospholipids) of the oleaginous fungus Cunninghamella echinulata was studied during the growth cycle. The lipid hydroperoxide content of total lipids increased during growth. Neutral lipids contained a small amount of hydroperoxides (0.78×10–4–5×10–4 µmol/mg), glycolipids plus sphingolipids contained large amounts of hydroperoxides (14×10–4–17.6×10–4 µmol/mg), while the hydroperoxide content of phospholipids increased greatly during growth (from 4.6×10–4 to 38×10–4 µmol/mg). In addition, the distribution of lipid hydroperoxides among the major phospholipid classes indicated that the neutral phospholipids, namely phosphatidylcholine and phosphatidylethanolamine, were more susceptible to peroxidation than the anionic ones (i.e. phosphatidylinositol and phosphatidylserine). A novel parameter, namely “specific lipid peroxidizability”, which is able to evaluate the susceptibility to peroxidation (peroxidizability) of each lipid fraction/class due to the nature of the lipid itself, was introduced. By using this parameter it was found that peroxidizability depended on the nature of the individual lipid rather than on its polyunsaturated fatty acid content.

Separation, detection, and quantification of hydroperoxides formed at side-chain and backbone sites on amino acids, peptides, and proteins

Hydroperoxides are major reaction products of radicals and singlet oxygen with amino acids, peptides, and proteins. However, there are few data on the distribution of hydroperoxides in biological samples and their sites of formation on peptides and proteins. In this study we show that normal-or reversed-phase gradient HPLC can be employed to separate hydroperoxides present in complex systems, with detection by postcolumn oxidation of ferrous xylenol orange to the ferric species and optical detection at 560 nm. The limit of detection (10–25 pmol) is comparable to chemiluminescence detection. This method has been used to separate and detect hydroperoxides, generated by hydroxyl radicals and singlet oxygen, on amino acids, peptides, proteins, plasma, and intact and lysed cells. In conjunction with EPR spin trapping and LC/MS/MS, we have obtained data on the sites of hydroperoxide formation. A unique fingerprint of hydroperoxides formed at α-carbon (backbone) positions has been identified; such backbone hydroperoxides are formed in significant yields only when the amino acid is part of a peptide or protein. Only side-chain hydroperoxides are detected with free amino acids. These data indicate that free amino acids are poor models of protein damage induced by radicals or other oxidants.

Stereochemistry of olefin and fatty acid oxidation. Part 2. Photosensitised oxidation of hexene and hepta-2,5-diene isomers

The stereochemistry of the photosensitised oxidation of hex-1-ene, cis- and trans-hex-2-ene, cis- and trans-hex-3-ene, and of the three geometrical isomers of hepta-2,5-diene, has been investigated by the reduction or hydrogenation of the hydroperoxides produced and analysis of the resulting allylic or saturated alcohols. The isomeric distribution of hydroperoxides from hexene isomers is that expected from the concerted ene reaction of singlet oxygen with the parent olefin oriented so as to favour the cis, cyclic process. In contrast to autoxidation, photosensitised oxidation of hepta-2,5-diene isomers produces a mixture of conjugated (67–70%) and nonconjugated (30–33%) hydroperoxides. The conjugated products formed are explicable in terms of the conformations of the parent dienes which have the least steric interactions.