The thiobarbituric acid (TBA) method of lipid hydroperoxide requires Fe catalyst to decompose the hydroperoxide to TBA-reactive secondary products during the reaction. In order to characterize the role of Fe catalyst, FeCl
3, ferritin, hemin, defatted tissue homogenate and whole tissue homogenate, were employed for the reaction of methyl linoleate hydroperoxide (MLHPO) with TBA. The results are as follows : 1) Non-heme iron (FeCl
3, ferritin) could play as an effective catalyst at a wide range of concentration, while hemin in high concentration suppressed the color intensity of optimum condition. The maximum efficiency of Fe catalyst existing in tissue homogenate lies between non-heme iron and hemin. 2) The TBA reaction catalyzed by FeCl
3 or ferritin was inhibited by EDTA, but not by BHT. The reverse effect of BHT and EDTA was observed in hemin or tissue homogenate catalysts. 3) The TBA reaction catalyzed with fresh FeCl
3 proceeded regardless the absence of oxygen, while the TBA value obtained with aged FeCl
3, ferritin, hemin or tissue homogenate was significantly depressed under anaerobic conditions. 4) The catalytic activity in rat liver tissue was distributed similarly among all subcellular fractions, but 105000×g pellet showed the highest effect per unit of protein.
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