| Popis: |
Human exposure to weak, environmental electromagnetic fields (EMF) is widespread. Furthermore, a statistically significant association exists between residential proximity to high-voltage power lines and an increased risk of childhood Leukaemia. Most possible mechanisms involving such weak EMF are overwhelmed by the body’s own thermal ‘noise’. The radical pair mechanism (RPM), however, can circumvent thermodynamic considerations by magnetic field (MF)-induced changes in reaction rate. A ‘magnetic field effect (MFE) stopped-flow spectrophotometer’ has been successfully constructed and tested in-house to enable robust investigations with enzyme reaction systems involving RP intermediates. A commercial instrument was modified by reengineering the assembly that houses the 20 μl reaction cell from non-magnetic materials (Delrin and aluminium). Adjustable MF pulses (≤ 37 mT) are generated for a user-definable period within the cell volume by a bespoke pair of Helmholtz coils and a pulsed power supply. A previously published MFE in a horseradish peroxidase catalyzed reaction was chosen as a biological test system. However, the field-dependence, including the unique low-field feature, was not reproduced. Reanalysis of the original data uncovered a number of problems, the most significant being: 1) the method and analysis were insensitive to the reported changes; 2) the proposed RP are entirely notional. Stopped-flow MFE studies with adenosylcobalamin (AdoCbl)-dependent ethanolamine ammonia lyase (EAL), conducted by the same authors, were also revisited. The original method, used to identify the magnetically-sensitive step as C"Co homolysis, was found instead to be rate-limited by cofactor binding. The protocol was redesigned, but still no MFE observed. However, one was observed in the photolysis rate of both free AdoCbl and holo- EAL in absence of substrate. Together, these results suggest RP stabilization upon substrate binding, which has implications for the enormous catalytic power of AdoCbl-dependent enzymes. Two Human enzymes were also screened for MFEs, with negative outcomes. |
