Bulau Patrick, Zakrzewicz Dariusz, Kitowska Kamila, Leiper James, Gunther Andreas, Grimminger Friedrich, Eickelberg Oliver
Lung Center, University of Giessen School of Medicine, Aulweg 123, D-35329 Giessen, Germany.
Am J Physiol Lung Cell Mol Physiol. 2007 Jan;292(1):L18-24. doi: 10.1152/ajplung.00076.2006. Epub 2006 Aug 4.
Protein arginine methylation is catalyzed by a family of enzymes called protein arginine methyltransferases (PRMTs). Three forms of methylarginine have been identified in eukaryotes: monomethylarginine (l-NMMA), asymmetric dimethylarginine (ADMA), and symmetric dimethylarginine (SDMA), all characterized by methylation of one or both guanidine nitrogen atoms of arginine. l-NMMA and ADMA, but not SDMA, are competitive inhibitors of all nitric oxide synthase isoforms. SDMA is eliminated almost entirely by renal excretion, whereas l-NMMA and ADMA are further metabolized by dimethylarginine dimethylaminohydrolase (DDAH). To explore the interplay between methylarginine synthesis and degradation in vivo, we determined PRMT expression and DDAH activity in mouse lung, heart, liver, and kidney homogenates. In addition, we employed HPLC-based quantification of protein-incorporated and free methylarginine, combined with immunoblotting for the assessment of tissue-specific patterns of arginine methylation. The salient findings of the present investigation can be summarized as follows: 1) pulmonary expression of type I PRMTs was correlated with enhanced protein arginine methylation; 2) pulmonary ADMA degradation was undertaken by DDAH1; 3) bronchoalveolar lavage fluid and serum exhibited almost identical ADMA/SDMA ratios, and 4) kidney and liver provide complementary routes for clearance and metabolic conversion of circulating ADMA. Together, these observations suggest that methylarginine metabolism by the pulmonary system significantly contributes to circulating ADMA and SDMA levels.
蛋白质精氨酸甲基化由一类称为蛋白质精氨酸甲基转移酶（PRMTs）的酶催化。在真核生物中已鉴定出三种甲基精氨酸形式：单甲基精氨酸（l-NMMA）、不对称二甲基精氨酸（ADMA）和对称二甲基精氨酸（SDMA），它们的特征均为精氨酸的一个或两个胍基氮原子发生甲基化。l-NMMA和ADMA是所有一氧化氮合酶同工型的竞争性抑制剂，但SDMA不是。SDMA几乎完全通过肾脏排泄清除，而l-NMMA和ADMA则由二甲基精氨酸二甲胺水解酶（DDAH）进一步代谢。为了探究体内甲基精氨酸合成与降解之间的相互作用，我们测定了小鼠肺、心脏、肝脏和肾脏匀浆中的PRMT表达和DDAH活性。此外，我们采用基于高效液相色谱的方法对蛋白质结合型和游离甲基精氨酸进行定量，并结合免疫印迹法评估精氨酸甲基化的组织特异性模式。本研究的主要发现可总结如下：1）I型PRMTs的肺表达与蛋白质精氨酸甲基化增强相关；2）肺中ADMA的降解由DDAH1进行；3）支气管肺泡灌洗液和血清中的ADMA/SDMA比值几乎相同；4）肾脏和肝脏为循环ADMA的清除和代谢转化提供了互补途径。这些观察结果共同表明，肺系统对甲基精氨酸的代谢显著影响循环中ADMA和SDMA的水平。
