Nagababu Enika
Integrated Vascular Biology Laboratory, Department of Anesthesiology and Critical Care Medicine, Johns Hopkins Medical Institutions, 720 Rutland Ave, Ross 1150, Baltimore, MD 21205, United States; Molecular Dynamics Section, National Institute on Aging, Baltimore, MD 21224, United States.
Free Radic Biol Med. 2016 Dec;101:296-304. doi: 10.1016/j.freeradbiomed.2016.09.015. Epub 2016 Sep 28.
S-nitrosothiols (SNO) perform many important functions in biological systems, but the mechanism by which they are generated in vivo remains a contentious issue. Nitric oxide (NO) reacts with thiols to form SNO only in the presence of a molecule that will accept an electron from either NO or the thiol. In this study, we present evidence that ferriheme accepts an electron from NO or glutathione (GSH) to generate S-nitrosoglutathione (GSNO) in vitro under anaerobic or hypoxic (2% O) conditions. Ferriheme formed charge transfer-stable complexes with NO to form ferriheme-NO (heme-Fe(II)-NO) and with GSH to form ferriheme-GS (heme-Fe(II)-GS) under anaerobic conditions. The reaction between GSH and the heme-Fe(II)-NO complex or between NO and the heme-Fe(II)-GS complex resulted in simultaneous reductive ferriheme nitrosylation (heme-Fe(II)NO) and the generation of GSNO. Thus, ferriheme is readily reduced to ferroheme in the presence of NO and GSH together, but not with either individually. The reaction between NO and the heme-Fe(II)-GS complex to generate GSNO occurred more rapidly than NO was consumed by endothelial cells, but not red blood cells. In addition, pretreatment of endothelial cells with ferriheme or the ferriheme-GS complex generated SNO upon addition of NO under hypoxic conditions. The results of this study raise the possibility that in vivo, ferriheme can complex with GSH to form ferriheme-GS complex (heme-Fe(II)-GS), which rapidly reacts with NO to generate GSNO under intracellular oxygen levels. The GSNO formation by this mechanism is more efficient than any other in vitro mechanism(s) reported so far.
S-亚硝基硫醇（SNO）在生物系统中发挥着许多重要功能，但其在体内生成的机制仍是一个有争议的问题。一氧化氮（NO）仅在存在能从NO或硫醇接受电子的分子时，才会与硫醇反应形成SNO。在本研究中，我们提供证据表明，在厌氧或低氧（2% O₂）条件下，高铁血红素在体外可从NO或谷胱甘肽（GSH）接受电子以生成S-亚硝基谷胱甘肽（GSNO）。在厌氧条件下，高铁血红素与NO形成电荷转移稳定的复合物以形成高铁血红素-NO（血红素-Fe(II)-NO），并与GSH形成高铁血红素-GS（血红素-Fe(II)-GS）。GSH与血红素-Fe(II)-NO复合物之间的反应或NO与血红素-Fe(II)-GS复合物之间的反应导致同时发生还原性高铁血红素亚硝化（血红素-Fe(II)NO）并生成GSNO。因此，高铁血红素在NO和GSH同时存在时很容易还原为亚铁血红素，但单独与其中任何一种存在时则不然。NO与血红素-Fe(II)-GS复合物反应生成GSNO的速度比内皮细胞消耗NO的速度快，但红细胞消耗NO的速度则不然。此外，在内皮细胞中用高铁血红素或高铁血红素-GS复合物预处理后，在低氧条件下添加NO时会生成SNO。本研究结果提出了一种可能性，即在体内，高铁血红素可与GSH结合形成高铁血红素-GS复合物（血红素-Fe(II)-GS），该复合物在细胞内氧水平下与NO快速反应生成GSNO。通过这种机制形成GSNO比迄今为止报道的任何其他体外机制都更有效。
