Relaxing effects of formamide on glycerinated muscle fibers and on myosin B suspension

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Abstract
Acetone induces a reversible relaxation of glycerinated muscle fibers (I). We found that formamide is equally effective. Since the dielectric constant of formamide is larger and that of acetone is smaller than that of water, the change in the dielectric constant of the fiber medium after adding organic solvents has little to do with the mechanism of this organic solvent-induced relaxation. That ITP can substitute for ATP in this relaxation suggests that organic solvents, when they induce a relaxation, act on the contractile protein rather than on ATP. Comparing the relaxing effect of 11 different organic solvents, the authors propose a working hypothesis based on the assumption of a specific interaction between organic solvents and the contractile protein. Formamide in-duces a "clearing" response of myosin B suspensions which is an in vitro model of muscle relaxation. Effects of Mg, Ca, and ionic strength (KC1) on this clearing response are studied in comparison with the effects of these on EDTA -induced relaxation. It is then shown that the formamide-induced clearing response is less specific than the EDTA-induced clearing response with regard to the requirements for ATP and Mg.