Foster A C, White R J, Schwarcz R
J Neurochem. 1986 Jul;47(1):23-30. doi: 10.1111/j.1471-4159.1986.tb02826.x.
In mammalian peripheral organs, 3-hydroxyanthranilic acid oxygenase (3HAO), catalyzing the conversion of 3-hydroxyanthranilic acid to quinolinic acid, constitutes a link in the catabolic pathway of tryptophan to NAD. Because of the possible involvement of quinolinic acid in the initiation of neurodegenerative phenomena, we examined the presence and characteristics of 3HAO in rat brain tissue. A simple and sensitive assay method, based on the use of [carboxy-14C]3-hydroxyanthranilic acid as a substrate, was developed and the enzymatic product, [14C]quinolinic acid, identified by chromatographic and biochemical means. Kinetic analysis of rat forebrain 3HAO revealed a Km of 3.6 +/- 0.5 microM for 3-hydroxyanthranilic acid and a Vmax of 73.7 +/- 9.5 pmol quinolinic acid/h/mg tissue. The enzyme showed pronounced selectivity for its substrate, since several substances structurally and metabolically related to 3-hydroxyanthranilic acid caused less than 25% inhibition of activity at 500 microM. Both the Fe2+ dependency and the distinct subcellular distribution (soluble fraction) of brain 3HAO indicated a close resemblance to 3HAO from peripheral tissues. Examination of the regional distribution in the brain demonstrated a 10-fold variation between the region of highest (olfactory bulb) and lowest (retina) 3HAO activity. The brain enzyme was present at the earliest age tested (7 days postnatum) and increased to 167% at 15 days before reaching adult levels. Enzyme activity was stable over extended periods of storage at -80 degrees C. Taken together, these data indicate that measurements of brain 3HAO may yield significant information concerning a possible role of quinolinic acid in brain function and/or dysfunction.
在哺乳动物外周器官中，3-羟基邻氨基苯甲酸加氧酶（3HAO）催化3-羟基邻氨基苯甲酸转化为喹啉酸，它是色氨酸分解代谢途径至烟酰胺腺嘌呤二核苷酸（NAD）过程中的一个环节。由于喹啉酸可能参与神经退行性病变的起始过程，我们检测了大鼠脑组织中3HAO的存在情况及其特性。我们开发了一种基于使用[羧基-14C]3-羟基邻氨基苯甲酸作为底物的简单灵敏的检测方法，并通过色谱和生化方法鉴定了酶促产物[14C]喹啉酸。对大鼠前脑3HAO的动力学分析显示，3-羟基邻氨基苯甲酸的米氏常数（Km）为3.6±0.5微摩尔，喹啉酸的最大反应速度（Vmax）为73.7±9.5皮摩尔喹啉酸/小时/毫克组织。该酶对其底物表现出明显的选择性，因为几种在结构和代谢上与3-羟基邻氨基苯甲酸相关的物质在500微摩尔时对活性的抑制作用小于25%。脑3HAO对Fe2+的依赖性以及独特的亚细胞分布（可溶性部分）表明它与外周组织中的3HAO非常相似。对脑内区域分布的检测表明，3HAO活性最高的区域（嗅球）和最低的区域（视网膜）之间存在10倍的差异。脑酶在最早检测的年龄（出生后7天）就已存在，并在15天时增加到167%，之后达到成年水平。酶活性在-80℃长期储存期间保持稳定。综上所述，这些数据表明，对脑3HAO的测量可能会产生有关喹啉酸在脑功能和/或功能障碍中可能作用的重要信息。
