Anisotropic magnetic field effects in the re-oxidation of cryptochrome in the presence of scavenger radicals

Abstract

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Radical triads, not pairs, may explain effects of hypomagnetic fields on neurogenesis

“…Similar radical triad models have been suggested in the context of the cryptochrome compass sense [ 21 , 22 , 28 , 29 ]. For these systems, theoretical studies have predicted enhanced directional magnetosensitivity over the RPM [ 28 ], resilience to fast relaxation of one of the radicals of the triad [ 29 ] and functionality in the presence of electron-electron dipolar coupling [ 21 , 22 ], which are unavoidable for immobilized radicals, as assumed to underpin the cryptochrome compass. These fortuitous traits are linked to a spin-selective scavenging reaction of one of the radicals of the primary pair by the “scavenger radical”, via the so-called chemical Zeno effect [ 30 ].…”

“…In neurons, the primary established role of ascorbic acid is to scavenge ROS generated during synaptic activity and neuronal metabolism eventually yielding dehydroascorbic acid (DHA), typically via A •− , as the persistent radical intermediate [27]. Similar radical triad models have been suggested in the context of the cryptochrome compass sense [21,22,28,29]. For these systems, theoretical studies have predicted enhanced directional magnetosensitivity over the RPM [28], resilience to fast relaxation of one of the radicals of the triad [29] and functionality in the presence of electron-electron dipolar coupling [21,22], which are unavoidable for immobilized radicals, as assumed to underpin the cryptochrome compass.…”

“…Here, a i and b i label quantum states of radical i and we have introduced the partial trace over the superoxide-spin as ŝðtÞ ¼ Tr 2 ½rðtÞ�, i.e., ha 1 ; a 3 jŝðt; OÞjb 1 ; b 3 i ¼ ha 1 ; "; a 3 jrðt; OÞjb 1 ; "; b 3 i þ ha 1 ; #; a 3 jrðt; OÞjb 1 ; #; b 3 i. Tracing out the superoxide in Eq (1) subject to the aforementioned conditions yields the reduced equation of motion for ŝðtÞ in the Hilbert space of particles 1 and 3 [22]:…”

“…Here, we aim to demonstrate that the ostensible drawbacks of the radical pair model can be overcome in the framework of a radical triad mechanism (R3M) [ 21 , 22 ], which extends the by a third radical derived from a radical scavenger (see Fig 1B ; details provided below). Here, we consider the ascorbyl radical (A •− ; monodehydroascorbic acid) in this role, predominantly for concreteness, but also inspired by the abundance of ascorbic acid in neurons, its established function [ 23 ], and its favourable hyperfine structure, which is known to give rise to a large low field sensitivity [ 24 , 25 ].…”

Ab initio derivation of flavin hyperfine interactions for the protein magnetosensor cryptochrome

“…The latter reaction has been suggested to underpin magnetoreception in the dark. [10][11][12][13][14] While there is ongoing debate about the identity [15][16][17] of the partner radical and even the number [18][19][20][21][22] of radicals involved, the flavin radical, either protonated or in is anionic form, is a central cornerstone of all models.…”