STUDIES ON THE CHARACTERIZATION OF FISH SKIN LIPOXYGENASE

用凝胶层析法对新鲜沙丁鱼皮中提取的水溶组分进行了分级，并对每个蛋白质峰对亚油酸的促氧化活性进行了评估。得到两个活性峰，两个峰均为血红素蛋白。这些氧化原蛋白在不同条件下与亚油酸反应，还原后分析生成的氧化产物。两种馏分形成的过氧化氢的异构体组成均为9-和13-过氧化氢的混合物，其比例约为6/4，这一比例与自氧化几乎相似，对13-氢过氧化氢没有明显的选择性。13-氢过氧化氢被发现是一种外消旋混合物。从这些结果中，没有得到特异性地形成13-S-氢过氧化氢的脂氧合酶。经离子交换层析和电泳法进一步纯化，确定为肌红蛋白和血红蛋白。这两种HEM蛋白可以分解过氧化氢形成挥发性的羰基，从而产生鱼腥味。

Water soluble-fractions extracted from fresh sardine skins were fractionated by gel chromatography and each proteinous peaks were assessed for the prooxidant activities on linoleic acid. Two active peaks were obtained and both peaks were found to be heme proteins. These prooxidant proteins were reacted with linoleic acid under various conditions and the formed oxidation products were analyzed after reduction. The isomeric composition of hydroperoxides formed with both fractions were the mixtures of 9-and 13-hydroperoxides with the ratio of approximately 6/4. This ratio was almost similar to that of autoxidation and no preference on 13-hydroperoxide was observed. The 13-hydroperoxide was found to be a racemic mixture. From these results, no lipoxygenase which specifically forms 13-S-hydroperoxide was not obtained. The prooxidant fractions were further purified by ion-exchange chromatography and electrophoresis and found to be myoglobin and hemoglobin. These two hem proteins could decompose hyudroperoxides to form volatile carbonyls responsible for fishy off flavor.