How Many Myosins per Cross-Bridge? I. Flight Muscle Myofibrils from the Blowfly, Sarcophaga bullata

Abstract

Cross-bridges project from the myosin filaments in groupings which repeat every 14.5 nm along the filament shaft. We are going to call this repeating group of projections a "crown." Now, we share a general belief that each cross-bridge represents one myosin molecule (two S1 subunits) and we thought that we might be able to prove it with favorable material and techniques. In vertebrate striated muscle, it is still typical to speak in terms of two cross-bridges per crown, although there seems to be enough myosin to supply four molecules per crown (Huxley, 1963). When an insect fibrillar flight muscle was clearly seen in thin sections to display four cross-bridges per crown (Reedy, 1968), it seemed attractive to consider such a grouping for vertebrate muscle. However the insect muscle story already had its own anomaly in the matter of myosin to cross-bridge correspondence. For Chaplain and Tregear (1966) estimated that the...