The Role of Iron in Peroxidation of Polyunsaturated Fatty Acids in Liposomes

摘要

This work investigated iron-catalyzed lipid oxidation in marine phospholipid liposomes.Oxygen consumption was used as a method to study lipid oxidation at pH 5.5 and 30 °C.The relationship between consumed oxygen and amount of peroxides (PV) and thiobarbituric reactive substances (TBARS) formed showed that both Fe~(2+) and Fe~(3+) catalyzed lipid oxidation.When Fe~(2+) was added to liposomes at a concentration of approximately 10 mu M,an initial drop in dissolved oxygen (oxygen uptake rate >258 mu M/min),followed by a slower linear oxygen uptake (oxygen uptake rate 4-6 /Ml min),was observed.Addition of Fe~(3+) induced only the linear oxygen uptake.The initial fast drop in dissolved oxygen was due to oxidation of Fe~(2+) to Fe~(3+) by preexisting lipid peroxides (rate 79 mu M Fe~(2+)/min).Fe~(3+) is reduced by peroxides to Fe~(2+) at a slow rate (0.25 mu M Fe~(3+)/min at 30 °C) in a pseudo-first-order reaction.The redox cycling between Fe~(2+) and Fe~(3+) leads to an equilibrium between Fe~(2+) and Fe~(3+) resulting in a linear oxygen uptake.During the linear oxygen uptake,the interaction of Fe~(3+) with lipid peroxide is the rate-limiting factor.Both alkoxy and peroxy radicals are formed by breakdown of peroxides by Fe~(2+) and Fe~(3+).These radicals react with fatty acids giving lipid radicals reacting with oxygen.