Salyers K L, Cullum M E, Zile M H
Department of Food Science & Human Nutrition, Michigan State University, East Lansing 48824-1224.
Biochim Biophys Acta. 1993 Nov 7;1152(2):328-34. doi: 10.1016/0005-2736(93)90265-2.
Retinoyl beta-D-glucuronide is a biologically active metabolite of retinoic acid. The kinetics of UDP-glucuronosyltransferase-catalyzed biosynthesis of retinoyl beta-D-glucuronide was examined in rat liver and intestinal native microsomes incubated with [3H retinoic acid incorporated into liposomes. The product was identified by cochromatography with authentic all-trans retinoyl beta-D-glucuronide, by hydrolysis with beta-D-glucuronidase, and by mass spectrometry. In vitamin A-sufficient rats the apparent Km values for all-trans-retinoic acid were 173 microM and 125 microM, and the apparent Vmax, 62 and 41 pmol/min per mg, for small intestinal and liver microsomes, respectively. In vitamin A-deficient rats repleted with all-trans-retinyl acetate, the apparent Km (91 microM) and Vmax (53 pmol/min per mg) for intestinal microsomes were in range of those of vitamin A-sufficient rats. The similarities in the kinetic parameters for UDP-glucuronosyltransferase in small intestinal mucosa and liver suggest that the reactions are catalyzed by the same enzyme. In vitamin A-deficient rats given a large amount all-trans-retinoic acid (1.2 mmol/day for 3 days) the apparent Km was 105 microM and Vmax, 127 pmol/min per mg of intestinal microsomal protein. We conclude that the kinetics of intestinal retinoic acid glucuronidation are not characteristic of simple detoxification reactions. Retinoyl glucuronide may be important in mediating retinoic acid metabolism and function.
视黄酰β-D-葡萄糖醛酸是视黄酸的一种生物活性代谢产物。在与掺入脂质体的[3H]视黄酸一起孵育的大鼠肝脏和肠道天然微粒体中，研究了UDP-葡萄糖醛酸基转移酶催化的视黄酰β-D-葡萄糖醛酸生物合成的动力学。通过与 authentic全反式视黄酰β-D-葡萄糖醛酸共色谱、用β-D-葡萄糖醛酸酶水解以及质谱法鉴定产物。在维生素A充足的大鼠中，全反式视黄酸的表观Km值分别为173μM和125μM，小肠和肝脏微粒体的表观Vmax分别为62和41 pmol/min per mg。在补充了全反式视黄酯的维生素A缺乏大鼠中，小肠微粒体的表观Km（91μM）和Vmax（53 pmol/min per mg）在维生素A充足大鼠的范围内。小肠黏膜和肝脏中UDP-葡萄糖醛酸基转移酶动力学参数的相似性表明，这些反应由同一种酶催化。在给予大量全反式视黄酸（1.2 mmol/天，共3天）的维生素A缺乏大鼠中，表观Km为105μM，Vmax为127 pmol/min per mg小肠微粒体蛋白。我们得出结论，肠道视黄酸葡萄糖醛酸化的动力学并非简单解毒反应的特征。视黄酰葡萄糖醛酸可能在介导视黄酸代谢和功能方面很重要。
