LARMOR PRECESSION AS A MECHANISM FOR THE DETECTION OF STATIC AND ALTERNATING MAGNETIC-FIELDS

The Larmor theorem predicts that applying a magnetic field B to a particle of mass m and charge q which is under the influence of a strong central force leads to the superposition of a uniform precession of angular frequency w(L) = qB/(2m) about the direction of the field on the original motion. This imposes an axial symmetry on the original motion even though the energy of interaction of the ion with the field is negligible compared with its original energy. This could provide a mechanism by which a biological system detects the direction of a magnetic field. On the assumption that the effectiveness of a calcium binding enzyme such as calmodulin depends on its shape and thus in detail on the direction of vibration of the bound ion, the catalysed kinetics are shown to depend upon the amplitude of an applied magnetic field. Small amplitude alternating magnetic fields applied at an angle to a static field are shown to be very effective in altering the imposed symmetry in a frequency dependent manner. The mechanism has considerable immunity from noise because the vibrating ion is shielded within the cavity, it is sensitive only to a narrow band of disturbing frequencies and the precession rate does not depend on the frequency or amplitude of the vibrator.