Structures of bilirubin conjugates synthesized in vitro from bilirubin and uridine diphosphate glucuronic acid, uridine diphosphate glucose or uridine diphosphate xylose by preparations from rat liver.
作者信息
Fevery J, Leroy P, Van de Vijver M, Heirwegh K P
出版信息
Biochem J. 1972 Sep;129(3):635-44. doi: 10.1042/bj1290635.
In incubation mixtures containing digitonin-activated or untreated preparations from rat liver, albumin-solubilized bilirubin as the acceptor substrate and (a) UDP-glucuronic acid, (b) UDP-glucose or (c) UDP-xylose as the sugar donor, formation of the following ester glycosides was demonstrated: with (a), bilirubin beta-d-monoglucuronoside, with (b), bilirubin beta-d-monoglucoside and with (c), bilirubin monoxyloside or mixtures of the mono-and di-xyloside. 2. With UDP-glucuronic acid prolonged incubation and variation of the composition of the incubation mixtures yielded equimolar amounts of azodipyrrole (I) and azodipyrrole beta-d-monoglucuronoside (II) after treatment of the incubation mixtures with the diazonium salt of ethyl anthranilate. The azo-derivatives were identified by t.l.c. by reference to known compounds and by the following chemical tests. After ammonolysis the conjugated azo-derivative (II) yielded d-glucuronic acid and the carboxylic acid amide of azodipyrrole, indicating transfer of a glucuronic acid residue to the carboxylic acid groups of bilirubin. The beta-d-configuration of the sugar moiety and binding at C-1 were demonstrated by enzymic hydrolysis tests. 3. Analogous evidence established the structure of the reaction product obtained with UDP-glucose as the sugar donor, as bilirubin beta-d-monoglucoside. 4. With UDP-xylose as the sugar donor xylosyl transfer to the carboxylic acid groups of bilirubin with attachment at C-1 was demonstrated in an analogous way. A beta-d-configuration is considered very likely, but requires confirmation. 5. Monoxyloside formation was predominant at pH7.4, whereas at decreasing pH values increasing fractions of the substrate were converted into the dixyloside. Prolonged incubation, low concentrations of bilirubin and high concentrations of UDP-xylose favoured diconjugate formation. The available evidence supports the synthesis sequence: bilirubin --> bilirubin monoxyloside --> bilirubin dixyloside.
摘要
在含有洋地黄皂苷激活的或未经处理的大鼠肝脏制剂、白蛋白增溶胆红素作为受体底物以及（a）尿苷二磷酸葡糖醛酸、（b）尿苷二磷酸葡萄糖或（c）尿苷二磷酸木糖作为糖供体的孵育混合物中，证实形成了以下酯糖苷：与（a）形成胆红素β - d - 单葡糖醛酸苷，与（b）形成胆红素β - d - 单葡糖苷，与（c）形成胆红素单木糖苷或单木糖苷与双木糖苷的混合物。2. 以尿苷二磷酸葡糖醛酸为底物，延长孵育时间并改变孵育混合物的组成，在用邻氨基苯甲酸乙酯重氮盐处理孵育混合物后，产生了等摩尔量的偶氮二吡咯（I）和偶氮二吡咯β - d - 单葡糖醛酸苷（II）。通过薄层层析并参照已知化合物以及通过以下化学试验鉴定了这些偶氮衍生物。氨解后，共轭偶氮衍生物（II）产生d - 葡糖醛酸和偶氮二吡咯的羧酸酰胺，表明葡糖醛酸残基转移到了胆红素的羧酸基团上。通过酶促水解试验证实了糖部分的β - d - 构型以及在C - 1位的结合。3. 类似的证据确定了以尿苷二磷酸葡萄糖作为糖供体获得的反应产物的结构为胆红素β - d - 单葡糖苷。4. 以尿苷二磷酸木糖作为糖供体，以类似的方式证实了木糖基转移到胆红素的羧酸基团上并连接在C - 1位。认为很可能是β - d - 构型，但需要进一步证实。5. 在pH7.4时主要形成单木糖苷，而在pH值降低时，底物转化为双木糖苷的比例增加。延长孵育时间、低浓度的胆红素和高浓度的尿苷二磷酸木糖有利于双共轭物的形成。现有证据支持合成顺序：胆红素→胆红素单木糖苷→胆红素双木糖苷。
