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Aspects of iron-catalyzed lipid oxidation in fish sarcoplasmic reticulum
Abstract
In the presence of ADP and histidine, iron bound in increasing amounts to sarcoplasmic reticulum (SR) of fish over the range of 25-250 $\mu$M FeCl$\sb3$. Binding of iron was not reversible either by washing in water or after oxidation of the membrane lipid. There was no difference in the rate of lipid oxidation measured as TBA-reactive substances catalyzed by iron bound to the sarcoplasmic reticulum or by iron in the soluble phase of the assay medium when expressed on an iron basis. In addition, soluble and bound iron were similar with respect to both inhibition of their ability to catalyze lipid oxidation by thiourea and their generation of hydroxyl free radicals measured by production of methane sulfinic acid (MSA) from dimethyl sulfoxide. Iron generated a greater amount of hydroxyl free radicals in the presence of histidine than in a series of other histidine analogs as measured by production of MSA. Hydroxyl free radical production reached a constant value when histidine concentration was 1 mM or greater. Lipid oxidation stimulated by combinations of Fe$\sp{3+}$ and Fe$\sp{2+}$ at different ratios in the presence of ADP and histidine indicated that Fe$\sp{2+}$ is the initiator in this lipid oxidation system. The lag phase was increased by increasing Fe$\sp{2+}$ concentration and decreased by increasing SR concentration or using an aged SR. In enzymic system, NaCl prolonged the lag phase. While in non-enzymic system using ascorbate as the reducing agent, NaCl shortened the lag phase. Addition of either NADH or Fe$\sp{2+}$ to the medium after the oxidation had ceased caused another oxidative reaction with no lag phase. Depletion of natural antioxidant in SR could be a reason causing the reduction of lag phase in aged SR since almost all the tocopherol present in fresh SR was lost after 9 days storage. Oxidation of Fe$\sp{2+}$ occurred at the same time or slightly preceded lipid oxidation of freshly prepared SR. This did not relate to the concentration of SR or Fe$\sp{2+}.$ On the other hand, autoxidation of Fe$\sp{2+}$ in the presence of ADP and histidine was much slower than the oxidation of Fe$\sp{2+}$ during SR lipid oxidation. No lag phase was observed during the autoxidation of Fe$\sp{2+}$.
Subject Area
Biochemistry
Recommended Citation
Huang, Chen-Huei, "Aspects of iron-catalyzed lipid oxidation in fish sarcoplasmic reticulum" (1991). Doctoral Dissertations Available from Proquest. AAI9207413.
https://scholarworks.umass.edu/dissertations/AAI9207413