Effects of disorder and motion in a radical pair magnetoreceptor

Abstract

A critical requirement in the proposed chemical model of the avian magnetic compass is that the molecules that play host to the magnetically sensitive radical pair intermediates must be immobilized and rotationally ordered within receptor cells. Rotational disorder would cause the anisotropic responses of differently oriented radical pairs within the same cell to interfere destructively, while rapid molecular rotation would tend to average the crucial anisotropic magnetic interactions and induce electron spin relaxation, reducing the sensitivity to the direction of the geomagnetic field. So far, experimental studies have been able to shed little light on the required degree of ordering and immobilization. To address this question, computer simulations have been performed on a collection of radical pairs undergoing restricted rigid-body rotation, coherent anisotropic spin evolution, electron spin relaxation and spin-selective recombination reactions. It is shown that the ordering and motional constraints necessary for efficient magnetoreception can be simultaneously satisfied if the radical pairs are uniaxially ordered with a moderate order parameter and if their motional correlation time is longer than about a quarter of their lifetime.

Cryptochrome 2 mediates directional magnetoreception in cockroaches

“…Another important condition is that sensory molecules should optimally be aligned in the same direction within the receptor cells, in order that the stochastic effects of freely rotating molecules would be eliminated (51). Such a condition could be met by cytoskeletal anchoring to the membrane, or by at least partial immobilization within the cells (52).…”

Photoreceptor-based magnetoreception: optimal design of receptor molecules, cells, and neuronal processing

“…In the decade following, a significant body of work, both experimental and theoretical (Stass et al 2000;Weaver et al 2000;Timmel et al 2001;Woodward et al 2001;Weaver 2002;Cintolesi et al 2003;Henbest et al 2004;Ritz et al 2004Ritz et al , 2009Vink & Woodward 2004;O'Dea et al 2005;Rodgers et al 2005Rodgers et al , 2007Thalau et al 2005;Vaughan & Weaver 2005;Shakirov et al 2006;Solov'yov et al 2007;Woodward & Vink 2007;Efimova & Hore 2008;Maeda et al 2008;Miura & Murai 2008;Solov'yov & Schulten 2009;Hill & Ritz 2010;Lau et al 2010), has advanced our information and understanding of how a putative radical-pair magnetoreceptor should be designed so as to be well suited to detect the geomagnetic field. Behavioural studies have provided more information about the functional properties of magnetic compasses in a variety of animals (Rappl et al 2000;Wiltschko et al 2000aWiltschko et al ,b, 2001Wiltschko et al , 2002bWiltschko et al , 2003aWiltschko et al , 2004aWiltschko et al ,b, 2005Wiltschko et al , 2006Wiltschko et al , 2007aÅ kesson et al 2001;Phillips et al 2001Phillips et al , 2002Muheim et al 2002Muheim et al , 2006Irwin & Loh...…”

The quantum needle of the avian magnetic compass

“…Only a handful has attempted to deal with realistic, multinuclear radical pairs (10,16,17,20). The other critical ingredient in such simulations is the lifetime of the electron spin coherence: if the spins dephase completely before the radicals have a chance to react, there can be no effect of an external magnetic field (35). Several studies have assumed, explicitly or implicitly, that the spin coherence persists for about a microsecond, i.e., the reciprocal of the electron Larmor frequency (1.4 MHz) in a 50-μT field (9,10,17,20).…”