Studies on Enzyme System of Tryptophan Metabolism in Fish Liver

1. 研究了鱼肝脏中参与色氨酸代谢的几种酶。犬尿氨酸途径是动物色氨酸代谢的主要途径。催化犬尿氨酸途径第一步的鱼肝色氨酸吡咯酶活性较低，且不被血凝素激活。对虹鳟鱼肝脏中犬尿氨酸途径第二酶芳酰甲酰胺酶进行了纯化，并与牛酶进行了性能比较。鱼酶被色氨酸抑制。这表明鱼的犬尿氨酸途径是由色氨酸调控的，色氨酸是该途径的第一底物。羟氰胺加氧酶活性与氨基羧酸半醛脱羧酶活性的比值表明，虹鳟鱼的nad1形成途径效率极低。鱼肝提取物表现出明显的色氨酸羟化酶活性，色氨酸羟化酶是血清素途径中的第一种酶。羟化酶对色氨酸的Km值低于吡咯酶。看来，5 -羟色胺途径的重要性超过了犬尿氨酸途径。

1. Several enzymes which are involved in the metabolism of tryptophan in fish liver were investigated.2. It is known that the kynurenine pathway is the major route in tryptophan metabolism in animals. The activity of fish liver tryptophan pyrrolase which catalyzes the first step in kynurenine pathway was comparatively low, and it was not activated by hematin.3. Arylformamidase, the second enzyme in kynurenine pathway, of the rainbow trout liver was purified and its properties were compared to those of the cattle enzyme. The fish enzyme was inhibited by tryptophan. This suggests that the kynurenine pathway of fish is regulated by tryptophan, the first substrate of the pathway.4. The ratio of hydroxyanthranillate oxygenase activity to aminocarboxymuconic semialdehyde decarboxylase activity indicated that the NAD-forming pathway is exceedingly inefficient in the rainbow trout.5. Fish liver extract exhibited an apparent activity of tryptophan hydroxylase, the first enzyme in the serotonine pathway. The Km value of hydroxylase to tryptophan was lower than that of pyrrolase. It appears that the importance of the serotonine pathway exceeds that of the kynurenine pathway.