Miller D A, DeLuca H F
Arch Biochem Biophys. 1986 Jan;244(1):179-86. doi: 10.1016/0003-9861(86)90107-4.
All-trans-retinoic acid is metabolized in vitro to a biologically active metabolite, retinoyl-beta-glucuronide. We have studied the synthesis of this metabolite in vitro. The identity of the product was established by cochromatography on reverse-phase high-performance liquid chromatography, beta-D-glucuronidase hydrolysis, and fast atom bombardment and collisionally activated decomposition/fast atom bombardment mass spectrometry. The formation of retinoyl-beta-glucuronide is catalyzed by a UDP-glucuronosyltransferase with apparent Km's of 54.7 microM for all-trans-retinoic acid and 2.4 mM for UDP-glucuronic acid. The reaction requires enzyme, UDP-glucuronate, and no other factor. It is strongly inhibited by millimolar concentrations of coenzyme A. The specific activity of UDP-glucuronosyltransferase is greatest in the liver and least in the kidney of those tissues examined. The specific activity of the enzyme is increased by vitamin A deficiency. The increased specific activity observed in the vitamin A-deficient rat liver is uncharacteristic of retinoic acid inactivation enzymes; therefore, retinoyl-beta-glucuronide may be of functional importance.
全反式维甲酸在体外可代谢为一种生物活性代谢产物——视黄酰-β-葡萄糖醛酸苷。我们已对该代谢产物的体外合成进行了研究。通过反相高效液相色谱共色谱法、β-D-葡萄糖醛酸酶水解以及快原子轰击和碰撞激活分解/快原子轰击质谱法确定了产物的身份。视黄酰-β-葡萄糖醛酸苷的形成由一种UDP-葡萄糖醛酸基转移酶催化，该酶对全反式维甲酸的表观Km值为54.7微摩尔，对UDP-葡萄糖醛酸的表观Km值为2.4毫摩尔。该反应需要酶、UDP-葡萄糖醛酸，不需要其他因素。它受到毫摩尔浓度辅酶A的强烈抑制。在所检测的组织中，UDP-葡萄糖醛酸基转移酶的比活性在肝脏中最高，在肾脏中最低。该酶的比活性因维生素A缺乏而增加。在维生素A缺乏的大鼠肝脏中观察到的比活性增加并非维甲酸失活酶的特征；因此，视黄酰-β-葡萄糖醛酸苷可能具有功能重要性。
