Ferric hemoglobin (metHb) and myoglobin (metMb), present at low levels in vivo, have been recently found to oxidize hydrogen sulfide (H₂S) in excess, thus potentially contributing to removal of toxic H₂S in blood and heart, respectively. Here, we present a kinetic and thermodynamic study of the reaction of metHb and metMb with H₂S under physiological conditions, i.e. at low H₂S concentrations and with protein in excess of H₂S. We show here that both proteins react with sub-stoichiometric H₂S:heme ratios following two processes: a fast reversible binding of H₂S to ferric heme that prevails at high H₂S and a slow heme reduction to the ferrous state that prevails at low H₂S. While these two processes are fast for metMb, H₂S-induced heme reduction is slow for metHb and the metHb-H₂S complex once formed is therefore relatively stable. We find that metHb binds H₂S reversibly and cooperatively with a pH-dependent ligand affinity that is within the physiological range of H₂S concentrations found in blood. Stopped-flow kinetics show identical association rate constants for H₂S at varying pH, demonstrating that H₂S and not HS⁻ enters the ferric heme pocket. Dissociation rates of the metHb-H₂S complex increase when decreasing pH, consistent with the pH-dependent affinity. Taken together, these data are consistent with a novel biological role of metHb as a H₂S carrier in the blood, in parallel with the oxygen carrier function of the much more abundant ferrous Hb. In contrast, metMb in the heart could participate to redox-signaling involving H₂S.

最近发现体内存在的三价铁血红蛋白（metHb）和肌红蛋白（metMb）会过量氧化硫化氢（H ₂ S），因此分别潜在地有助于去除血液和心脏中的有毒H ₂ S 。这里，我们提出metHb和metMb的用H的反应的动力学和热力学研究₂的生理条件下，即在低ħ ₂硫的浓度，并用过量H的蛋白₂ S.我们在这里表明，这两种蛋白质与子反应化学计量比的H ₂ S：血红素比率可通过以下两个过程进行：H ₂ S与三价铁血红素的快速可逆结合，在高H时占优势₂ S和在低H ₂ S时普遍存在的亚铁血红素缓慢还原。虽然这两个过程对于metMb快速，但是对于metHb H ₂ S诱导的血红素还原缓慢，并且一旦形成了metHb-H ₂ S复合物。因此相对稳定。我们发现metHb可逆地结合H ₂ S并与pH依赖性配体亲和力结合，该亲和力在血液中发现的H ₂ S浓度的生理范围内。停流动力学显示用于h相同结合速率常数₂ S中变化的pH，表明ħ ₂ S和不HS ^-进入铁血红素口袋。metHb-H _2的解离速率当降低pH时，S络合物增加，这与pH依赖性亲和力一致。综上所述，这些数据与作为血液中H ₂ S载体的metHb的新型生物学作用，以及更为丰富的亚铁Hb的氧载体功能相一致。相反，心脏中的metMb可能参与涉及H ₂ S的氧化还原信号传递。