Lamkemeyer Tobias, Paul Rüdiger J, Stöcker Walter, Yiallouros Irene, Zeis Bettina
Institut für Zoophysiologie, Westfälische Wilhelms-Universität, Hindenburgplatz 55, D-48143 Münster, Germany.
Biol Chem. 2005 Nov;386(11):1087-96. doi: 10.1515/BC.2005.125.
The haemoglobin (Hb) of Daphnia magna acclimated to different oxygen conditions was sampled, and in its natively assembled state it was separated by chromatofocusing. The Hb isoforms were analysed for their subunit composition under denaturating conditions by two-dimensional gel electrophoresis. The Hb system is suggested to consist of three predominant Hb aggregates, which are characterised by a specific subunit composition and synthesised in response to different ambient oxygen conditions. In normoxia, a dominant Hb aggregate (DmHbI) with a pI of 4.4-4.6 was composed of subunits B, C, E, F and G. In severe hypoxia, a different dominant Hb isoform (DmHbIII) with a pI of 5.7-5.9 was composed of subunits A, B, C, D, E and F. Further analyses in moderate hypoxia provided evidence for a third Hb isoform (DmHbII) composed of subunits B, C, D, E and F. Sequence alignment and homology modelling of the tertiary structure of the D. magna Hb domains 1 and 2 revealed functionally relevant substitutions of amino acid residues at positions B10, E7 and E11, which determine the functional properties of D. magna haemoglobin in terms of haem contact, oxygen binding and affinity. Both domains are predicted to possess the common haemoglobin fold, but helices C and D are not properly formed, and helix G is interrupted by a short coil.
对适应不同氧气条件的大型溞的血红蛋白（Hb）进行采样，并在其天然组装状态下通过色谱聚焦进行分离。通过二维凝胶电泳在变性条件下分析Hb亚型的亚基组成。研究表明，Hb系统由三种主要的Hb聚集体组成，它们具有特定的亚基组成，并根据不同的环境氧气条件进行合成。在常氧条件下，一种主要的Hb聚集体（DmHbI），其pI为4.4 - 4.6，由亚基B、C、E、F和G组成。在严重缺氧条件下，一种不同的主要Hb亚型（DmHbIII），其pI为5.7 - 5.9，由亚基A、B、C、D、E和F组成。在中度缺氧条件下的进一步分析为第三种Hb亚型（DmHbII）提供了证据，该亚型由亚基B、C、D、E和F组成。大型溞Hb结构域1和2的三级结构的序列比对和同源建模揭示了B10、E7和E11位置的氨基酸残基的功能相关替代，这些替代决定了大型溞血红蛋白在血红素接触、氧结合和亲和力方面的功能特性。预计这两个结构域都具有常见的血红蛋白折叠，但螺旋C和D形成不当，螺旋G被一个短线圈中断。
