Department of Biology, Northeastern University, Boston, MA, 02115, USA.
Department of Biology, Northeastern University, Boston, MA, 02115, USA.
Anal Biochem. 2020 Jun 15;599:113730. doi: 10.1016/j.ab.2020.113730. Epub 2020 Apr 11.
The Root Effect is to many species of fish what the Bohr Effect is to humans regarding the release of O from their hemoglobins at low pH. However, Root Effect hemoglobins accomplish this more extensively than human adult hemoglobin in order to satisfy the diverse oxygen requirements in fish. To understand this difference between fish and human hemoglobins, we studied their subunit interface strengths using very low (nanomolar) concentrations, referred to as nano gel filtration. Root Effect hemoglobins in their CO form dissociate in a tetramer-monomer equilibrium. In contrast, tetramers and dimers but no monomers are found for adult human hemoglobin consistent with its well known tetramer-dimer equilibrium. By analogy to the human variant Hb Kansas and a similar recombinant Hb, both of which readily release oxygen due to an unstable oxygenated structure, the mechanism proposed is that oxygenated Root Effect tetramers release their oxygen to form energetically stable deoxygenated tetramers rather than dissociate to energetically unfavorable oxygenated dimers with labile interfaces. In contrast, the strong binding of CO permits observation of dissociation to monomers, thus revealing an intrinsic property of Root Effect fish hemoglobins enabling it to function as an oxygen pump.
根效应（Root Effect）对于许多鱼类物种来说，就如同波尔效应（Bohr Effect）对于人类血红蛋白在低 pH 值下释放 O 一样。然而，根效应血红蛋白比人类成人血红蛋白更广泛地实现了这一点，以满足鱼类多样化的氧气需求。为了理解鱼类和人类血红蛋白之间的这种差异，我们使用非常低（纳摩尔）浓度的纳米凝胶过滤技术研究了它们的亚基界面强度。处于 CO 形式的根效应血红蛋白在四聚体-单体平衡中解离。相比之下，对于成人人类血红蛋白，只发现了四聚体和二聚体，而没有单体，这与它众所周知的四聚体-二聚体平衡一致。根据人类变体 Hb Kansas 和类似的重组 Hb 的类比，这两种变体由于不稳定的氧合结构都容易释放氧气，提出的机制是，氧合的根效应四聚体释放其氧气以形成能量稳定的脱氧四聚体，而不是解离成界面不稳定的能量不利的氧合二聚体。相比之下，CO 的强结合允许观察到单体的解离，从而揭示了根效应鱼类血红蛋白的固有特性，使其能够作为氧气泵发挥作用。
