On the Contraction of Myosin-Extracted Skinned Single Fibers with Active Myosin Fragments

Abstract

The shortening of myosin-extracted skinned single fibers (MESS fibers) was studied in detail under irrigations with myosin, heavy meromyosin (HMM), and myosin subfragment-1 (S-1). The MESS fibers were carefully prepared according to Tawada et al. (J. Biochem. (1976) 80, 121-127) with a modification as regards the extraction temperature. In addition, the fibers were kept at 40°C for more than 10min in order to inactivate any trace amount of myosin, if present. The MESS fibers were confirmed to recover their shortening ability when placed in myosin, HMM, and S-1 solutions, as reported by Oplatka et al. (Biochim. Biophys. Acta (1976) 440, 241-258). The velocity of the shortening was very slow but was proportional to the original length. A quasi-biphasic behavior was observed in the extent of the shortening of the MESS fibers, at least in heavy meromyosin solutions, with respect to the temperature as well as the concentration of Mg-ATP. The molecular mechanism of the shortening can be discussed in terms of the metachronal rotation model of myosin heads. It is pointed out that close parallels exist between the shortening of MESS fibers with heavy meromyosin and the active streaming of heavy meromyosin solutions in a stream cell (Yano, M. et al. (1978) J. Biochem. 84, 277-283; Yano, M. & Shimizu, H. (1978) J. Biochem. 84, 1087-1092; Shimizu, H. & Yano, M. (1978) J. Biochem. 84, 1093-1102). Therefore, the dynamic cooperativity among elementary cycles of the chemo-mechanical conversion seems to be an important factor in the shortening of MESS fibers.