STUDIES ON THE CHARACTERIZATION OF FISH SKIN LIPOXYGENASE

从新鲜沙丁鱼皮中提取的水溶性组分通过凝胶色谱法进行分级，并评估每个蛋白峰对亚油酸的促氧化活性。得到两个活性峰，发现这两个峰都是血红素蛋白。这些促氧化蛋白与亚油酸在各种条件下反应，并在还原后分析形成的氧化产物。用这两种馏分形成的氢过氧化物的异构体组成是9-和13-氢过氧化物的混合物，比例约为6/4。该比率几乎与自氧化的比率相似，并且没有观察到对13-氢过氧化物的偏好。发现13-氢过氧化物是外消旋混合物。从这些结果中，没有得到特异性形成13-S-氢过氧化物的脂氧合酶。通过离子交换色谱和电泳进一步纯化促氧化剂组分，发现是肌红蛋白和血红蛋白。这两种血红素蛋白可以分解过氧化氢，形成挥发性羰基，导致鱼腥味。

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.