Department of Biology, University Roma Tre, Roma, Italy.
FEBS J. 2010 Jun;277(11):2474-85. doi: 10.1111/j.1742-4658.2010.07662.x. Epub 2010 Apr 26.
Heme endows human serum albumin (HSA) with heme-protein-like reactivity and spectroscopic properties. Here, the kinetics and thermodynamics of reductive nitrosylation of ferric human serum heme-albumin [HSA-heme-Fe(III)] are reported. All data were obtained at 20 degrees C. At pH 5.5, HSA-heme-Fe(III) binds nitrogen monoxide (NO) reversibly, leading to the formation of nitrosylated HSA-heme-Fe(III) [HSA-heme-Fe(III)-NO]. By contrast, at pH >or= 6.5, the addition of NO to HSA-heme-Fe(III) leads to the transient formation of HSA-heme-Fe(III)-NO in equilibrium with HSA-heme-Fe(II)-NO(+). Then, HSA-heme-Fe(II)-NO(+) undergoes nucleophilic attack by OH(-) to yield ferrous human serum heme-albumin [HSA-heme-Fe(II)]. HSA-heme-Fe(II) further reacts with NO to give nitrosylated HSA-heme-Fe(II) [HSA-heme-Fe(II)-NO]. The rate-limiting step for reductive nitrosylation of HSA-heme-Fe(III) is represented by the OH(-)-mediated reduction of HSA-heme-Fe(II)-NO(+) to HSA-heme-Fe(II). The value of the second-order rate constant for OH(-)-mediated reduction of HSA-heme-Fe(II)-NO(+) to HSA-heme-Fe(II) is 4.4 x 10(3) M(-1) s(-1). The present results highlight the role of HSA-heme-Fe in scavenging reactive nitrogen species.
血红素赋予人血清白蛋白（HSA）血红素蛋白样反应性和光谱特性。本文报道了高铁人血清血红素白蛋白[HSA-heme-Fe(III)]还原亚硝化为亚硝基的动力学和热力学。所有数据均在 20°C 下获得。在 pH 5.5 下，HSA-heme-Fe(III)可逆地结合一氧化氮（NO），导致亚硝基化 HSA-heme-Fe(III)[HSA-heme-Fe(III)-NO]的形成。相比之下，在 pH≥6.5 时，向 HSA-heme-Fe(III)中添加 NO 导致 HSA-heme-Fe(III)-NO 与 HSA-heme-Fe(II)-NO(+)处于平衡状态的瞬态形成。然后，HSA-heme-Fe(II)-NO(+)通过 OH(-)的亲核攻击生成亚铁人血清血红素白蛋白[HSA-heme-Fe(II)]。HSA-heme-Fe(II)进一步与 NO 反应生成亚硝基化 HSA-heme-Fe(II)[HSA-heme-Fe(II)-NO]。HSA-heme-Fe(III)还原亚硝化的限速步骤由 OH(-)介导的 HSA-heme-Fe(II)-NO(+)还原为 HSA-heme-Fe(II)表示。OH(-)介导的 HSA-heme-Fe(II)-NO(+)还原为 HSA-heme-Fe(II)的二级速率常数的值为 4.4 x 10(3) M(-1) s(-1)。本研究结果强调了 HSA-heme-Fe 在清除活性氮物种中的作用。
