A new isoform of 11 beta-hydroxysteroid dehydrogenase in aldosterone target cells.
A new isoform of 11 beta-hydroxysteroid dehydrogenase in aldosterone target cells.
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DOI：
10.1016/s0021-9258(18)82044-0
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发表时间：
1993-05
期刊：
影响因子：
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通讯作者：
E. Rusvai;A. Náray-Fejes-Tóth
中科院分区：
文献类型：
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作者：
E. Rusvai;A. Náray-Fejes-Tóth
11 β-羟基类固醇脱氢酶被认为通过降解内源性糖皮质激素在醛固酮靶细胞中发挥重要作用，从而使醛固酮与相对非选择性的盐皮质激素受体结合。这种酶在肾醛固酮靶细胞中的生理学上重要的种类似乎在动力学和抗原性上不同于先前表征的肝酶。在这里，我们表明，11 β-类固醇脱氢酶在微粒体部分的分离肾集合管细胞具有Km为25.9 +/- 2.4 nM的皮质酮，约100倍低于大鼠肝酶。令人惊讶的是，集合管酶几乎完全利用NAD作为辅因子，而肝脏形式使用NADP。皮质酮转化为11-脱氢皮质酮的转化率分别为2.6 +/- 0.5和0.07 +/- 0.01 fmol/min/mg蛋白质，100 μ M的NAD和NADP，表明NAD相对于NADP的37.4 +/- 3.5倍偏好。实际上，11-脱氢皮质酮与NADH或NADPH均不转化为皮质酮，表明在集合管细胞中，酶仅在氧化方向上起作用。此外，11 β-类固醇脱氢酶活性受到终产物11-脱氢皮质酮的剂量依赖性抑制，而肝酶未显示终产物抑制。我们的结论是，肾集合管细胞，醛固酮的主要生理目标，保护循环糖皮质激素由迄今未描述的酶的11-脱氢酶家族，这不同于已知的肝酶具有显着更高的亲和力，皮质酮和不同的辅因子的要求。
11 beta-Hydroxysteroid dehydrogenase has been proposed to play an important role in aldosterone target cells by degrading endogenous glucocorticoids, thus allowing aldosterone to bind to the relatively nonselective mineralocorticoid receptor. The physiologically important species of this enzyme in renal aldosterone target cells appears to be kinetically and antigenically distinct from the previously characterized liver enzyme. Here we show that 11 beta-steroid dehydrogenase in the microsomal fraction of isolated renal collecting duct cells has a Km for corticosterone of 25.9 +/- 2.4 nM, about 100 times lower than the rat liver enzyme. Surprisingly, the collecting duct enzyme utilizes almost exclusively NAD as cofactor versus NADP used by the liver form. Conversion of corticosterone to 11-dehydrocorticosterone is 2.6 +/- 0.5 and 0.07 +/- 0.01 fmol/min/mg protein with 100 microM of NAD and NADP, respectively, demonstrating a 37.4 +/- 3.5-fold preference for NAD versus NADP. There is practically no conversion of 11-dehydrocorticosterone to corticosterone either with NADH or NADPH, indicating that in collecting duct cells the enzyme operates only in the direction of oxygenation. In addition, 11 beta-steroid dehydrogenase activity is dose dependently inhibited by the end product 11-dehydrocorticosterone while the liver enzyme does not show end product inhibition. We conclude that renal collecting duct cells, the major physiological targets of aldosterone, are protected from circulating glucocorticoids by a hitherto undescribed enzyme of the 11-dehydrogenase family, which differs from the known liver enzyme in having a significantly higher affinity for corticosterone and a different cofactor requirement.