Enzymatic spin-catalysis in flavin-containing oxidases and magnetic orientation of birds

O. O. Panchenko, B. F. Minaev


Introduction. The magnetic field of the Earth covers the entire globe and the closest space around it, which makes it possibleto provide information about the direction of magnetic flux lines. Humans use it with a compass to navigate and orient in the space of the ocean or airplane in the sky. Can birds and other animals also use the magnetic field of the Earth for orientation in space?

Purpose. To calculate spin density in individual radicals - anion radicals FAD and cation-radical tryptophan for radical pairs which are contained in cryptochromes of birds. On this basis, to evaluate the electron-nuclear hyperfine interactions of the Fermi contact type. To estimate the influence of magnetic field on the birds orientation through the neural net using the Hori theory.

Methods. The 3D visualization method of the HyperChem-7.51 calculation software for quantum-chemical modeling of FAD and tryptophan by the PM3 method and the Gaussian software for optimizing the FAD molecule by the exchange-correlation functional B3LYP/6-31G (d) were used.

Results. The values of charges and spin density on atoms in the corresponding anion- and cation- radicals are calculated. Such atomic charges clearly explain intermolecular interactions that occurs when the radicals are coordinated in the protein shell of the cryptochrome.

Taking into account the spin density in the anion- and cation-radicals of the cryptochrome RP, we have calculated the constants of the hyperfine interactions for all the nuclei of both radicals. Based on the theory of RP, an estimation of the T-S transition rate in a divided pair of radicals of an anion FAD and a tryptophan cation was performed. Our calculations confirm the general picture of the kinetics of spin transitions in the weak magnetic field proposed in the paper [1].

Conclusion. Quantum-chemical calculations of FAD confirm the theory of enzymatic spin-catalysis in oxidases due to the specific structure of the molecular orbitals of this molecule and of its oxidized and reduced forms. Similar calculations are applied for the cryptochrome radical pair.

The calculated atomic charges explain the strength of intermolecular interactions when the radicals are coordinated in the protein shell of the bird’s eyes cryptochrome.

Spin density at nitrogen atoms creates large values of hyperfine magnetic electron-nuclear interactions, which determines a sufficient rate constant value of the singlet-triplet transition, even in the weak magnetic field of the Earth.


flavinucleotides; FAD; cryptochromes; spin-orbit interaction; hypertonic EPR structure; electron-nuclear spin-spin interaction


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