Conversion of L-thyroxine to triiodothyronine in rat kidney homogenate.
Conversion of L-thyroxine to triiodothyronine in rat kidney homogenate.
复制标题
大鼠肾匀浆中 L-甲状腺素转化为三碘甲状腺原氨酸。
DOI：
10.1210/endo-102-2-612
复制
发表时间：
1978
期刊：
影响因子：
4.8
通讯作者：
I. Rosenberg
中科院分区：
文献类型：
--
作者：
P. Chiraseveenuprapund;U. Buergi;A. Goswami;I. Rosenberg
在磷酸盐-EDTA缓冲液中，大鼠肾匀浆始终催化添加的L-甲状腺素（T4）形成T3。通过纸层析和T3的RIA评估T3的形成。T4转化为T3似乎是酶促的，显示出最佳pH和温度（分别为pH 7.0和37 ℃）以及组织和时间依赖性。T3的形成不受叠氮化物、氰化物或过氧化氢酶的影响，也不依赖于氧气;事实上，在厌氧条件下，T4转化为T3的能力增强。透析匀浆保留了全部活性，并且证明不需要辅因子。铁螯合剂和巯基封闭剂的抑制作用，建议在T3从T4的酶促形成的铁和巯基基团的作用。肾脏形成T3的能力相当大，并随着T4浓度的增加而增加，在非常高的T4水平下约为2 nmol/g组织/h。表观Km估计为3 × 10（-6）M。T4转化为T3的抑制丙基硫氧嘧啶在微摩尔浓度，而甲巯咪唑，碘化物，锂盐没有影响。匀浆的酶活性与其颗粒成分，容易沉淀的馏分对应于质膜和线粒体是最活跃的，是不存在的细胞核和胞质溶胶。
Rat kidney homogenates, in phosphate-EDTA buffer, consistently catalyzed the formation of T3 from added L-thyroxine (T4). The formation of T3 was assessed by both paper chromatography and RIA of T3. Conversion of T4 to T3 appeared to be enzymatic, showing pH and temperature optima (pH 7.0 and 37 C, respectively) and tissue and time dependence. Formation of T3 was unaffected by azide, cyanide, or catalase, nor was it dependent upon oxygen; indeed, under anaerobic conditions conversion of T4 to T3 was enhanced. Dialyzed homogenate retained full activity, and no cofactor requirement was demonstrated. A role of iron and thiol groups in the enzymatic formation of T3 from T4 was suggested by the inhibitory action of iron chelators and thiol-blocking reagents. The capacity of kidney for T3 formation was considerable and increased with increasing T4 concentrations, being approximately 2 nmol/g tissue/h at very high T4 levels. The apparent Km was estimated to be 3 x 10(-6) M. The conversion of T4 to T3 was inhibited by propylthiouracil at micromolar concentrations whereas methimazole, iodide, and lithium salts were without effect. The enzymatic activity of the homogenates was associated with its particulate components, the readily sedimenting fractions corresponding to plasma membranes and mitochondria being most active, and was absent from nuclei and cytosol.