Subedi Harishchandra, Brasch Nicola E
Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242, USA and Division of Science, Mathematics, and Physical Education, Western Nebraska Community College, Scottsbluff, Nebraska 69361, USA.
School of Applied Sciences, Auckland University of Technology, Private Bag 92006, Auckland 1142, New Zealand.
Dalton Trans. 2016 Jan 7;45(1):352-60. doi: 10.1039/c5dt03459k.
There is accumulating evidence for the existence of HNO in biological systems. Compared with NO (˙NO), much less is known about the chemical and biochemical reactivity of HNO. Kinetic and mechanistic studies have been carried out on the reaction between the vitamin B12-derived radical complex cob(II)alamin (Cbl(II)˙, Cbl(II)) with the widely used HNO donor Piloty's acid (PA). A stoichiometry of 1 : 2 Cbl(II) : PA was obtained and PA decomposition to HNO and benzenesulfinate (C6H5SO2(-)) is the rate-determining step. No evidence was found for nitrite (Griess assay), ammonia (Nessler's test) or NH2OH (indooxine test) in the product solution, and it is likely that HNO is instead reduced to N2. A mechanism is proposed in which reduction of Cbl(II) by (H)NO results in formation of cob(I)alamin (Cbl(I)(-)) and ˙NO. The Cbl(I)(-) intermediate is subsequently oxidized back to Cbl(II) by a second (H)NO molecule, and Cbl(II) reacts rapidly with ˙NO to form nitroxylcobalamin (NOCbl). Separate studies on the reaction between Cbl(I)(-) and PA shows that this system involves an additional step in which Cbl(I)(-) is first oxidized by (H)NO to Cbl(II), which reacts further with (H)NO to form NOCbl, with an overall stoichiometry of 1 : 3 Cbl(I)(-) : PA. Experiments in the presence of nitrite for both systems support the involvement of a Cbl(I)(-) intermediate in the Cbl(II)/PA reaction. These systems provide the second example of oxidation of cob(I)alamin by (H)NO.
越来越多的证据表明生物系统中存在一氧化氮（HNO）。与一氧化氮（˙NO）相比，人们对HNO的化学和生化反应性了解较少。已对维生素B12衍生的自由基配合物钴胺素（II）（Cbl（II）˙，Cbl（II））与广泛使用的HNO供体皮洛蒂酸（PA）之间的反应进行了动力学和机理研究。得到了1:2的Cbl（II）:PA化学计量比，PA分解为HNO和苯亚磺酸盐（C6H5SO2(-)）是速率决定步骤。在产物溶液中未发现亚硝酸盐（格里斯试验）、氨（奈斯勒试验）或羟胺（吲哚酚试验）的证据，HNO可能被还原为N2。提出了一种机制，其中（H）NO还原Cbl（II）导致形成钴胺素（I）（Cbl（I）(-)）和˙NO。Cbl（I）(-)中间体随后被第二个（H）NO分子氧化回Cbl（II），Cbl（II）与˙NO迅速反应形成硝酰钴胺素（NOCbl）。对Cbl（I）(-)与PA之间反应的单独研究表明，该系统涉及一个额外的步骤，其中Cbl（I）(-)首先被（H）NO氧化为Cbl（II），Cbl（II）再与（H）NO进一步反应形成NOCbl，总的化学计量比为1:3的Cbl（I）(-):PA。在两个系统中亚硝酸盐存在下的实验支持了Cbl（I）(-)中间体参与Cbl（II）/PA反应。这些系统提供了（H）NO氧化钴胺素（I）的第二个例子。
