Peters W H, Jansen P L
J Hepatol. 1986;2(2):182-94. doi: 10.1016/s0168-8278(86)80077-0.
Human liver microsomal bilirubin UDP-glucuronyltransferase catalyzes formation of bilirubin mono- and diglucuronide. KmUDPGA and Vmax of the enzyme are 0.6 mM and 1.69 nmol/mg protein X min. In vitro, bilirubin readily dissolves in the microsomal lipid phase. Taking this into account a Kmbilirubin of 60.6 microM was found, which is much higher than the in vivo microsomal UCB concentration of human liver (2.9-11.4 microM). The total capacity of human liver to form bilirubin mono- and diglucuronide in vitro exceeds the in vivo mono- and diglucuronide production rates by a factor 8 to 10. Radiation-inactivation studies reveal that human liver microsomal bilirubin UDP-glucuronyltransferase is a tetrameric enzyme with a molecular mass of 209 000 +/- 20 000 Da. The complete tetrameric enzyme catalyzes both glucuronidation steps, formation of bilirubin monoglucuronide and conversion of mono- to diglucuronide. In its monomeric form, the enzyme with molecular mass of 55 000 +/- 1 500 Da catalyzes only the first step of bilirubin glucuronidation, the formation of bilirubin monoglucuronide.
人肝微粒体胆红素UDP-葡萄糖醛酸基转移酶催化胆红素单葡萄糖醛酸酯和双葡萄糖醛酸酯的形成。该酶的KmUDPGA和Vmax分别为0.6 mM和1.69 nmol/mg蛋白质×分钟。在体外，胆红素很容易溶解于微粒体脂质相中。考虑到这一点，测得胆红素的Km为60.6 μM，这远高于人肝微粒体中体内未结合胆红素的浓度（2.9 - 11.4 μM）。人肝在体外形成胆红素单葡萄糖醛酸酯和双葡萄糖醛酸酯的总能力比体内单葡萄糖醛酸酯和双葡萄糖醛酸酯的生成速率高8至10倍。辐射失活研究表明，人肝微粒体胆红素UDP-葡萄糖醛酸基转移酶是一种分子量为209 000 ± 20 000 Da的四聚体酶。完整的四聚体酶催化两个葡萄糖醛酸化步骤，即胆红素单葡萄糖醛酸酯的形成以及单葡萄糖醛酸酯向双葡萄糖醛酸酯的转化。以其单体形式存在时，分子量为55 000 ± 1 500 Da的该酶仅催化胆红素葡萄糖醛酸化的第一步，即胆红素单葡萄糖醛酸酯 的形成。
