Biological sensing of small field differences by magnetically sensitive
chemical reactions
Weaver JC, Vaughan TE, Astumian RD
Nature 405: 707-709, 8 June 2000
There is evidence that animals can detect small changes in the Earth's
magnetic field by two distinct mechanisms, one using the mineral magnetite
as the primary sensor and one using magnetically sensitive chemical
reactions. Magnetite responds by physically twisting, or even reorienting
the whole organism in the case of some bacteria, but the magnetic dipoles
of individual molecules are too small to respond in the same way. Here we
assess whether reactions whose rates are affected by the orientation of
reactants in magnetic fields could form the basis of a biological compass.
We use a general model, incorporating biological components and design
criteria, to calculate realistic constraints for such a compass. This
model compares a chemical signal produced owing to magnetic field effects
with stochastic noise and with changes due to physiological temperature
variation. Our analysis shows that a chemically based biological compass
is feasible with its size, for any given detection limit, being dependent
on the magnetic sensitivity of the rate constant of the chemical reaction.
