Englander J J, Rumbley J N, Englander S W
Department of Biochemistry & Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA, 19104-6059, USA.
J Mol Biol. 1998 Dec 18;284(5):1707-16. doi: 10.1006/jmbi.1998.2279.
To study allosteric mechanism in hemoglobin, a hydrogen-exchange method was used to measure ligand-dependent changes in structural free energy at defined allosterically sensitive positions. When the two alpha-subunits are CN-met liganded, effects can be measured locally, within the alpha-subunit, and also remotely, within the beta-subunit, even though the quaternary structure remains in the T conformation. When the two beta-subunits are liganded, effects occur at the same positions. The effects seen are the same, independently of whether ligands occupy the alpha-chain hemes or the beta-chain hemes. Control experiments rule out modes of energy transfer other than programmed cross-subunit interaction within the T-state. Cross-subunit transfer may depend on pulling the heme trigger (moving the heme iron into the heme plane) rather than on liganding alone.
为了研究血红蛋白中的变构机制，采用了氢交换方法来测量在特定变构敏感位置上配体依赖性的结构自由能变化。当两个α亚基被氰化高铁配体结合时，即使四级结构仍处于T构象，效应既可以在α亚基内局部测量，也可以在β亚基内远程测量。当两个β亚基被配体结合时，相同位置会出现效应。无论配体占据α链血红素还是β链血红素，所观察到的效应都是相同的。对照实验排除了T态内除了程序化的跨亚基相互作用之外的能量转移模式。跨亚基转移可能取决于拉动血红素扳机（将血红素铁移入血红素平面），而不仅仅取决于配体结合。
