Fluorescence microscope study of the binding of added C protein to skeletal muscle myofibrils.

Abstract

The binding of extra C protein to rabbit skeletal muscle myofibrils was investigated by fluorescence microscopy with fluorescein-labeled C protein or unmodified C protein plus fluorescein-labeled anti-C protein. Added C protein binds strongly to the I bands, which is consistent with its binding to F actin in solution. The binding to the I band is Ca regulated; it requires a free Ca ion concentration comparable to that which activates the myofibrillar ATPase. This increases the likelihood that C protein-actin interaction might be physiologically significant. When I band binding is suppressed, binding in the A band become evident. It appears to occur particularly near the M line, and possibly at the edges of the A band as well, suggesting that those parts of the thick filaments that lack C protein in vivo may nevertheless be capable of binding added C protein.