Butanedione Monoxime Suppresses Contraction and ATPase Activity of Rabbit Skeletal Muscle1

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Abstract
The effects of 2, 3-butanedione 2-monoxime (BDM) on mechanical responses of glycerinated fibers and the ATPase activity of heavy meromyosin (HMM) and myofibrils have been studied using rabbit skeletal muscle. The mechanical responses and the ATPase activity were measured in similar conditions (ionic strength 0.06–0.2 M, 0.4–4 mM MgATP, 0–20 mM BDM, 2–20°C and pH 7.0). BDM reversibly reduced the isometric tension, shortening speed, and instantaneous stiffness of the fibers. BDM also inhibited myofibrillar and HMM ATPase activities. The inhibitory effect on the relative ATPase activity of HMM was not influenced by the addition of actin or troponin-tropomyosin-actin. High temperature and low ionic strength weakened BDM's suppression of contraction of the fibers and the ATPase activity of contracting myofibrils, but not of the HMM, acto-HMM and relaxed myofibrillar ATPase activity. The size of the initial phosphate burst at 20°C was independent of the concentration of BDM. These results suggest that the suppression of contraction of muscle fibers is due mainly to direct action of BDM on the myosin molecules.

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