The large subunit of myosin (~2000 aa) that has the ATPase activity. The head region undergoes conformational change during the actin attachment/detachment cycle, each cycle involving hydrolysis of one ATP molecule, and it is this conformational change that converts energy into movement. In conventional filament-forming myosins (type II myosin) the head is attached via a hinge region to a tail domain that interacts laterally with other myosin tails to form the backbone of the thick filament In the nonmuscle myosins, the tail may attach to ‘cargo’ vesicles. In skeletal muscle there are seven heavy chain isoforms, two developmental, three in adult skeletal muscle, one also expressed in cardiac muscle, one expressed primarily in extrinsic eye muscles. Mutations in the gene for myosin heavy chain 9 lead to the May–Heggelin anomaly. Heavy meromyosin is a subfragment of the heavy chain of myosin II. See also myosin light chains.
Subjects: Medicine and Health.