Transient EPR Spectroscopy and Mechanical Transients in Muscle Fibers

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The muscle is a prototype of a biological engine; the burning of its chemical fuel, ATP, results in the generation of the mechanical force. How this happens is not very well understood. It is known that molecules involved (myosin and actin) form long inter-digitating filaments (similar to overlapping combs) which are bridged by the portion of the myosin molecule. According to a popular model, the bridge between the filaments burns ATP which causes pivoting rotation of the bridge, thus creating the strain between the filaments. The strain can be relieved by the sliding of the filaments with respect to each other shortening the muscle length. However, the evidence for such a pivoting of the bridge is missing. Dr. Fajer proposes to use electron paramagnetic resonance (EPR) spectroscopy, a technique sensitive to the orientational and dynamic chanees of the molecules. Since the muscle does not have an EPR signal, Dr. Fajer intends to bind a paramagnetic probe to the bridge portion of the myosin which does not perturb muscle function but will report specifically the behavior of the bridge. He will stimulate muscle to produce force and the same time record orientational and dynamic changes of the bridge. Such an approach will directly correlate the structural changes and the function of muscle.