We examined myosin of fast and slow skeletal rat muscles regenerating after ischemia and bupivacaine injection in denervated limbs. Four days after injury two-dimensional gel electrophoresis revealed the presence of the embryonic light chain in the myosin isolated from the portion of muscle showing a homogeneous population of new small fibers by histological examination. Two weeks after injury this subunit was absent, whereas the two light chains, LC1F and LC2F, became prominent. One month after injury the still denervated soleus muscle maintained this light chain pattern. Gel electrophoresis in native condition of the myosin and peptide mapping of electrophoretically purified heavy chains confirmed that the muscle regenerating in absence of the nerve accumulated a myosin that had the general features of a fast, not slow, myosin but contained definite differences from the former.
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