meromyosin

Fragments of skeletal-muscle myosin II generated by trypsin cleavage. Heavy meromyosin (HMM) has the ATPase activity and the hinge region; light meromyosin (LMM) is the tail region, mostly α-helical, that interacts with other LMMs to bundle myosin into the thick filament. HMM will bind to F-actin in the absence of ATP to produce a characteristic arrowhead pattern in electronmicrographs. Further cleavage of HMM with papain yields S1 and S2 subfragments, the former having the ATPase activity, the latter acting as a flexible hinge.