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Bioelectromagnetism

FIGURE 4.2 Ethanolamine ammonia-lyase stopped-fow kinetic study (Grissom, 1995, modifed from Harkins

and Grissom, 1995). Te magnetic feld dependence of the frst-order rate of appearance of Cbl^II with unlabeled eth­

anolamine is shown. Standard error bars may be smaller than the plotted symbol. Identical rates are observed with

unlabeled and deuterated ethanolamine. (Reproduced with permission from Grissom, 1995; Harkins and Grissom,

1995, Copyright 1995, American Chemical Society.)

alamin-5′-deoxyadenosyl} radical pair. Spin-selective recombination to adenosylcobalamin decreased

the enzyme catalytic efciency kcat/Km by 16% at 760 mT.

Klevanik (1996) examined the magnetic feld efects on primary reactions of Photosystem (PS)

I by measuring changes of the fuorescence yield in preparations isolated from the cyanobacterium

Synechococcus elongatus. Photoaccumulation of the reduced phylloquinone A1 (the electron acceptor

of PS I) in the presence of dithionite under anaerobic conditions led to an increase of chlorophyll (Chl)

fuorescence yield and appearance of magnetic feld efects (Klevanik, 1996). A magnetic feld efect has

been found which is characterized by half-saturation values of the order of ~ 2.5 mT (Klevanik, 1996).

Te addition of salts of monovalent and divalent cations to the suspension signifcantly modifed the

profle of the magnetic feld dependence (Klevanik, 1996). Te modifcation of the magnetic feld efect

by salts is ascribed to conformational changes in the PS I reaction center that afect the dipolar and/or

spin exchange coupling in the radical pair P700⁺ A0

− (P700, the primary electron donor of PS I that best

absorbs light at a wavelength of 700 nm; A0, the primary electron acceptor of PS I) (Klevanik, 1996).

Injection of neutral red into suspensions of samples containing reaction centers in the state P700 A0

A1

red gives rise to light-induced fuorescence quenching and disappearance of the magnetic feld efect

(Klevanik, 1996). In the dark, the high fuorescence and the magnetic feld efect are restored (Klevanik,

1996). Tese phenomena are ascribed to photoaccumulation of state P700 A0

− A1

red and a strong quench­

ing efect of the Chl an anion radical A0

− that closely resembles that of Pheo- in PS II (Klevanik, 1996).

Te magnetic felds have been shown to change radical concentrations (Batchelor et al., 1993; Grissom,

1995; Hayashi, 2004; Timmel and Henbest, 2004). Spin modulation in the RPM is considered a plausible

explanation of how the static magnetic felds including the geomagnetic feld (GMF) can alter the chem­

istry of reactions and cause biological efects (Barnes and Greenebaum, 2015). Te RPM is used to exem­

plify how applied magnetic felds weaker in strength than typical hyperfne interactions can infuence

the yields and kinetics of recombination reactions of free radicals in the solution (Timmel et al., 1998).

“Spin-correlated radical pairs” can undergo coherent mixing between singlet (antiparallel) and triplet

(parallel) spin states, which have diferent reactive fates, and this mixing process can be modulated by

magnetic felds (Steiner and Ulrich, 1989; Woodward et al., 2009). Here triplet products are chemically

diferent from the singlet products and thus may play a role in magnetoreception.

Te RPM is a promising hypothesis to explain the mystery of the navigation of birds (Zhang et al.,

2015). Tis theoretical study has demonstrated the role of weak magnetic felds play in the product

yields of the radical pairs. In addition, this type of study has inspired scientists to design highly efective