Post irradiation temporal profiles as a tool to investigate the mechanism of lipid peroxidation in compartmentalized systems

A methodology is proposed to investigate the origin of the autoacceleration frequently observed when the oxidation of lipids takes place in compartmen talized systems. The method is based on the evaluation of post-irradiation effects and time profiles of oxygen consumption when the irradiation is re- initiated after a dark period. The proposal is experimentally tested in the oxidation of egg-yolk phosphatidylcholine (PC) vesicles initiated by decom position of a water soluble free radical source. Three sceneries and the expected time profiles of oxygen consumption are pr oposed to explain the origin of the autoacceleration effect: (i) initial in hibiton by remainig low levels of (unknown) antioxidants; (ii) autoaccelera tion due to contribution of peroxidized products to the initiation rate; an d (iii) a lag time due to the long reactions times required to reach the st eady-state condition when the oxidation takes place in compartmentalized sy stems. The results obtained are consistent with case (i). The conclusion reached i s considered to be relevant in the context that it allows differentiation b etween spurious effects [case (i)] and intrinsic effects [cases (ii) and (i ii)]. This can contribute to a better understanding of the factors involved in the interpretation of the kinetic and mechanistic aspects of lipid pero xidation in compartmentalized systems.