Role of exchange and dipolar interactions in the radical pair model of the avian magnetic compass
Role of exchange and dipolar interactions in the radical pair model of the avian magnetic compass
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DOI：
10.1529/biophysj.107.119362
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发表时间：
2008-03-01
影响因子：
3.4
通讯作者：
Hore, P. J.
中科院分区：
文献类型：
--
作者：
Efimova, Olga;Hore, P. J.
目前还不清楚候鸟如何感知地球磁场作为指南针信息的来源。一种建议是，磁感受器涉及一种光化学反应，其产物产量对外部磁场很敏感。具体地说，黄素-色氨酸自由基对被认为是通过光诱导沿着固定在视网膜中的隐色素黄素蛋白中的三个色氨酸残基的链进行顺序电子转移而形成的。电子塞曼与地球磁场(类似于50mU T)的相互作用，受到自由基内各向异性磁相互作用的调制，导致产物产量取决于受体的取向。根据公认的理论，为了使自由基间的自旋-自旋相互作用足够弱，以允许类似于50µT的场产生显著的效应，需要将自由基间的~gt；3.5 nm分开。利用量子力学模拟，这里表明，在2.0+/-0.2 nm的小得多的间隔处，仍然可以预期产物产率的实质性变化，其中交换和偶极相互作用的影响部分抵消。隐色素中的末端黄素-色氨酸自由基对的间隔类似于1.9 nm，因此是充当COMPASS机制的磁受体的理想位置。
It is not yet understood how migratory birds sense the Earth's magnetic field as a source of compass information. One suggestion is that the magnetoreceptor involves a photochemical reaction whose product yields are sensitive to external magnetic fields. Specifically, a flavin-tryptophan radical pair is supposedly formed by photoinduced sequential electron transfer along a chain of three tryptophan residues in a cryptochrome flavoprotein immobilized in the retina. The electron Zeeman interaction with the Earth's magnetic field (similar to 50 mu T), modulated by anisotropic magnetic interactions within the radicals, causes the product yields to depend on the orientation of the receptor. According to well-established theory, the radicals would need to be separated by > 3.5 nm in order that interradical spin-spin interactions are weak enough to permit a similar to 50 mu T field to have a significant effect. Using quantum mechanical simulations, it is shown here that substantial changes in product yields can nevertheless be expected at the much smaller separation of 2.0 +/- 0.2 nm where the effects of exchange and dipolar interactions partially cancel. The terminal flavin-tryptophan radical pair in cryptochrome has a separation of similar to 1.9 nm and is thus ideally placed to act as a magnetoreceptor for the compass mechanism.