Reinigung und charakterisierung einer löslichen uridin diphosphat-glucuronat: 17β-hydroxysteroid-glucuronyl-transferase beim menschen

K Dahm, H Breuer
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引用次数: 10

Abstract

The ground plasma (150 000 × g supernatant) of the human intestine contains a uridinediphosphate glucuronate glucuronyltransferase (EC 2.4.1.17) which catalyses exclusively the formation of 17β-glucuronides of oestriol, 17β-oestradiol and testosterone. This enzyme was found in the fractions obtained between 60 and 80% saturation of the ground plasma with ammonium sulphate; it could be separated from two other uridine diphosphate glucuronate glucuronyltransferases which, with oestriol as substrate, were capable of forming the 3-glucuronide and the 16α-glucuronide. The two latter enzymes were present in the fractions obtained at 0–30% and 30–60% saturation of the ground plasma with ammonium sulphate. The low specific activity of the enzyme catalysing the formation of the 3-glucuronide suggests the probability of its origin by microsomal leakage.

The kinetics of the uridinediphosphate glucuronate: 17β-hydroxysteroid glucuronyltransferase are described. The formation of the 17β-glucuronide of oestriol shows a maximum at pH 6.8. The Michaelis-Menten constant was found to be 3.5 · 10−4M, whereas the activation energy of the enzyme amounted to 12.2 kcal/mole.

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干洗店的特性的一个试验uridin diphosphat-glucuronat: 17β-hydroxysteroid-glucuronyl-transferase在人
人肠的碎血浆(150000 × g上清)含有尿二磷酸葡萄糖醛酸葡萄糖醛酸转移酶(EC 2.4.1.17),它专门催化17β-葡萄糖醛酸雌三醇、17β-雌二醇和睾酮的形成。这种酶存在于用硫酸铵研磨的血浆饱和度在60%到80%之间得到的馏分中;该酶与另外两种以雌三醇为底物的尿苷二磷酸葡萄糖醛酸葡萄糖醛酸转移酶分离,可生成3-葡萄糖醛酸和16α-葡萄糖醛酸。后两种酶存在于用硫酸铵研磨的血浆饱和度为0-30%和30-60%时得到的馏分中。催化3-葡糖苷形成的酶的低比活性表明它的起源可能是微粒体渗漏。描述了尿苷二磷酸葡萄糖醛酸:17β-羟基类固醇葡萄糖醛酸转移酶的动力学。雌三醇的17β-葡糖苷在pH值6.8时生成最大值。Michaelis-Menten常数为3.5·10−4M,酶的活化能为12.2 kcal/mol。
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