Abstract
Ca 2+-calmodulin-dependent myosin phosphorylation is studied here to assess magnetic field effects on Ca 2+ binding. The cell-free reaction mixture was chosen for the phosphorylation rate to be linear in time for several minutes, and to be rate limited by Ca 2+. To this end the ratio of substrate to enzyme was < 100:1 in order to slow the overall reaction rate, and the Ca 2+ concentration was well below saturation for calmodulin. The Ca 2+ concentration was varied from 1 to 7 μM with appropriate EGTA buffering. Phosphorylation was allowed to proceed for 5 min at 44 μT (ambient) and 200 μT (vertical). The results showed that phosphorylation increased up to 2× at 200 μT (vs. 44 μT) dependent upon [Ca 2+]. In addition, as [Ca 2+] approaches saturation for calmodulin, the magnetic field effect disappears. Effects between 1 and 5 μM Ca 2+ were analyzable using a Lineweaver-Burk plot, showing a negligible change in affinity, K D, and a relatively large increase in V MAX (1.8× at 200 μT vs. ambient) suggesting Ca 2+ binding kinetics are affected.
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