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Static, Low-Frequency, and Pulsed Magnetic Fields
Engström (2007). Several models describing the influence of magnetic field on kinetics
of enzymatic reactions that involve free radical–dependent chemistry have been elaborated. These models demonstrate that even subtle alterations in radical pair recombination kinetics induced by weak magnetic fields might lead to measurable effects on
enzyme activity (Eichwald and Walleczek 1996; Izmaylov, Tully, and Frisch 2009). Study
of the effects of magnetic field on radical pair reactions that may have biological consequences is important (Brocklehurst 2002). According to theoretical estimates, the
physical transduction step induced by low fields is not vulnerable to thermal perturbations (Walleczek 1995; Adair 1999). Regarding the spin states of radicals, the radical pair
theory predicts that an applied magnetic field perturbs the interconversion of the singlet
and triplet states, resulting in an increase in the proportion of the triplet state and thus
the free radical concentration (Brocklehurst 2002).
Therefore, knowing the effects of magnetic fields on free radical reactions is particularly important when considering human health and the relation of immunological and
neurodegenerative diseases and stress response. Several attempts have been made to
explore the parameters of free radical reactions occurring when living organisms, cells,
and biochemicals are exposed to magnetic fields.
Regarding magnetic spin effects in radical enzymatic reactions involving at least one
ROS, the Grissom research group (Harkins and Grissom 1994) showed experimentally
that the activity of the B 12 -dependent enzyme ethanolamine ammonia lyase changes
with exposure to SMFs of 100 mT. This finding is the first recorded SMF effect on an
enzyme-catalyzed reaction with known radical pair intermediates in a cell-free solution.
It is a milestone in biomagnetism research on free radicals. Extensive experiments have
also been carried out with the heme enzymes horseradish peroxidase (HRP) and cytochrome C oxidase. The Grissom research group reported that the rate of HRP increases
by 20% at fields as low as 1 mT (Taraban et al. 1997). However, a recent detailed reinvestigation by the Woodward research group (Jones, Scrutton, and Woodward 2006)
demonstrated that the reported effects of SMF on HRP were not observed up to 75 mT.
Instead, the same research group studied the radical recombination reaction of radicals
generated from the photolysis of 2-hydroxy-4’-(2-hydroxyethoxy)-2-methylpropiophenone (α-HP) on a microsecond timescale using time-resolved mid-infrared spectroscopy (Vink and Woodward 2004). The reaction was found to exhibit opposite biphasic
magnetic field dependencies at 2 and 21 mT, and the effect at low fields was the first such
observation for neutral free radicals in isotropic solution.
Mohtat et al. (1998) examined the behavior of radical pairs derived by hydrogen
abstraction of the triplet state of benzophenone and some of its derivatives from
bovine serum albumin, human serum albumin, and calf thymus deoxyribonucleic
acid (DNA). The SMF strength was as high as 150 mT with durations as long as
10 milliseconds. The results of this study indicated that radical pair behavior is sensitive to magnetic fields, and this effect can be interpreted by using the theory of free
radical recombination.
The Hore research group researched the weak SMF effects on free radical recombination reactions (Till et al. 1998; Timmel et al. 1998). Using the triplet state of
benzophenone as a convenient source of pairs, the Hore research group examined
the effects of weak (1–2 mT) SMF on radical recombination reactions in micelles