Thiyl radical-induced cis/trans-isomerization of methyl linoleate in methanol and of linoleic acid residues in liposomes.
OBJECTIVE
To investigate the role of a thiol-containing biologically active compound in lipid peroxidation of membranes.


METHODS
Thiyl radicals were generated from 3-(2-mercaptoethyl)quinazoline-2,4(1H,3H)-dione (MECH) using pulse radiolysis and gamma-radiolysis in aqueous and alcoholic solutions saturated with N2O. The products were analysed by 1H NMR and by HPLC.


RESULTS
THE thiyl radicals abstract bisallylic hydrogens from [cis-9, cis-12]-methyl linoleate, yielding a pentadienyl radical. In the absence of oxygen, a thiyl radical-induced cis/trans-isomerization leads to linoleic-type isomers. These chain-type isomerization reactions can occur with the long living pentadienyl radical, followed by a 'repair' reaction of the attached thiol, and with the thiyl radical adduct with a double bond of the fatty acid residue.


CONCLUSIONS
The results show that the mechanism of cis/trans-isomerization is an integral part of the thiyl radical attack on polyunsaturated fatty acids in homogeneous solutions and in bilayers.
Schwinn
J
J
Research Unit Time-resolved Spectroscopy, Leipzig, Germany.
Sprinz
H
H
Drössler
K
K
Leistner
S
S
Brede
O
O
D002851:Chromatography, High Pressure Liquid; D005609:Free Radicals / Q000737:chemistry; D005720:Gamma Rays; D007536:Isomerism; D019787:Linoleic Acid / Q000737:chemistry*; D008041:Linoleic Acids / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D000432:Methanol; D011675:Pulse Radiolysis; D011799:Quinazolines / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry*
D005609:Free Radicals; D008041:Linoleic Acids; D008081:Liposomes; D011799:Quinazolines; D013438:Sulfhydryl Compounds; C086987:3-(2-mercaptoethyl)quinazoline-2,4(1H,3H)-dione; C005575:methyl linoleate; D019787:Linoleic Acid; D000432:Methanol