Abstract

Haptoglobin (Hp) counterbalances the adverse effects of extra-erythrocytic hemoglobin (Hb) trapping the αβ dimers of Hb. In turn, the Hp:Hb complexes display heme-based reactivity. Here, the kinetics of cyanide and carbon monoxide dissociation from ferrous-ligated Hp:Hb complexes are reported at pH 7.0 and 20.0 °C. Cyanide dissociation from Hp1-1:Hb(II)-CN⁻ and Hp2-2:Hb-CN⁻ has been followed upon the dithionite-mediated conversion of ferric to ferrous-ligated Hp:Hb complexes. Values of k_on for the dithionite-mediated reduction of Hp1-1:Hb(III)-CN⁻ and Hp2-2:Hb(III)-CN⁻ are (7.3 ± 1.1) × 10⁶ M⁻¹ s⁻¹ and (6.2 ± 1.0) × 10⁶ M⁻¹ s⁻¹, respectively. Values of the first-order rate constant (i.e., h) for cyanide dissociation from Hp1-1:Hb(II)-CN⁻ and Hp2-2:Hb(II)-CN⁻ are (1.2 ± 0.2) × 10⁻¹ s⁻¹ and (1.3 ± 0.2) × 10⁻¹ s⁻¹, respectively. CO dissociation from Hp:Hb(II)-CO complexes has been followed by replacing CO with NO. Values of the first-order rate constant (i.e., l) for CO dissociation from Hp1-1:Hb(II)-CO are (1.4 ± 0.2) × 10⁻² s⁻¹ and (6.2 ± 0.8) × 10⁻³ s⁻¹, and those from Hp2-2:Hb(II)-CO are (1.3 ± 0.2) × 10⁻² s⁻¹ and (7.3 ± 0.9) × 10⁻³ s⁻¹. Values of k_on, h, and l correspond to those reported for the R-state of tetrameric Hb and isolated α and β chains. This highlights the view that the conformation of the Hb αβ-dimers bound to Hp1-1 and Hp2-2 matches that of the R-state of the Hb tetramer. Furthermore, unlike ferric Hb(III), ligated ferrous Hb(II) does not show an assembly-linked structural change.

Graphic abstract

中文翻译：

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亚铁人类触珠蛋白：血红蛋白（II）配合物分解氰化物和一氧化碳的动力学。

摘要

血红蛋白（Hp）可以抵消红细胞外血红蛋白（Hb）捕获Hb的αβ二聚体的不利影响。反过来，Hp：Hb络合物显示出基于血红素的反应性。在此，据报道在pH 7.0和20.0°C下氰化和一氧化碳从铁连接的Hp：Hb络合物中解离的动力学。从HP1-1氰化物离解：HB（II）-CN ^-和HP2-2：HB-CN ^-一直沿袭时的三价铁向亚铁结扎Hp的连二亚硫酸盐介导的转化：血红蛋白复合物。的值ķ_上为HP1-1的连二亚硫酸盐介导的还原：HB（III）-CN ^-和HP2-2：HB（III）-CN ^-是（7.3±1.1）×10 ⁶ 中号^-1 小号^-1和（6.2±1.0）×10分别为⁶  M ^-1  s ^-1。一阶速率常数（即，值ħ），用于从HP1-1氰化物离解：HB（II）-CN ^-和HP2-2：HB（II）-CN ^-是（1.2±0.2）×10 ^-1  s ^-1和（1.3±0.2）×10 ^-1  s ^-1。从Hp：Hb（II）-CO络合物中解离CO后，用NO代替CO。CO从Hp1-1：Hb（II）-CO上解离的一级速率常数（l）的值为（1.4±0.2）×10 ^-2  s ^-1和（6.2±0.8）×10 ^-3  s ^-1，和来自Hp2-2：Hb（II）-CO的那些是（1.3±0.2）×10 ^-2  s ^-1和（7.3±0.9）×10 ^-3  s ^-1。的值ķ_上，ħ，和升对应于所报道的四聚体血红蛋白的R-状态和分离α和β链。这突出了这样一种观点，即与Hp1-1和Hp2-2结合的Hbαβ-二聚体的构象与Hb四聚体的R-态的构象相匹配。此外，与三价铁（III）不同，连接的亚铁（Hb）（II）没有显示出与组装相关的结构变化。

图形摘要