Myosin light chain functions.

The two regulatory light chains (RLC) of fast-twitch skeletal muscle myosin from rabbit are digested proteolytically at different rates. In purified actomyosin where the heads bind to actin in rigor, both RLC are digested at the same rate. Removal of both RLC does not affect the ATPase activities of myosin. Morphological studies by the electron microscope on spread and rotary shadowed myosin preparations as well as hydrodynamic studies by gel filtration technique revealed that upon removal of both RLC the shape of the head portions changes, the heads of one molecule tend to form intramolecular aggregation and, in addition, intermolecular aggregates, mostly dimers, are formed. These interactions are hydrophobic in nature and cannot readily be dissociated. These results could imply that one of the functions of the RLC is to keep the two heads of an individual myosin molecule apart from one another in muscle.