Binding of myosin cross-bridges to thin filaments of rabbit skeletal muscle.

Cross-linking of myosin subfragment 1 (S1) with a molar excess of actin in vitro reveals the presence of an actin-S1-actin complex. It is absolutely essential that actin be present in molar excess over S1 so that the decoration of F-actin with S1 be incomplete. However, the excess of actin may not be available in the overlap zone of sarcomeres of skeletal muscle. We therefore found it necessary to test for the presence of the actin-S1-actin complex in vivo. Myofibrils from rabbit skeletal muscle were reacted with zero-length cross-linker, the products were resolved by polyacrylamide gel electrophoresis and analyzed by Western blots using antibodies against actin and against heavy and light chains of myosin. The cross-linking produced the evidence of formation of actin-S1-actin complex.