Dependence of the length of the heavy chain of chymotryptic subfragment 1 on the temperature of myosin digestion.

Limited digestion of filamentous myosin with chymotrypsin at 0 degrees C in the absence of divalent cations generates two forms of subfragment 1 (S1), with heavy chains of 95 kDa and 98 kDa. The difference is at the C-terminal end of the chain. The 98 kDa form prevails, in contrast to the preparations obtained by digestion at room temperature which consist of the shorter species and only traces of the longer one. The results support the idea of a temperature-dependent conformational transition at the head-rod junctional region of the myosin heavy chain.