With regards to human anatomy myosin and actin constitute the basic functional unit of a muscle fiber, called sarcomere, playing a role in muscle contraction.
[2] Light meromyosin has a long, straight portion in the “tail” region.
Heavy meromyosin (HMM) is a protein chain terminating in a globular head portion/cross bridge.
HMMS-1 has an actin binding site and ATP binding site (myosin ATPase) that determines the rate of muscle contraction when muscle is stretched.
Light and heavy meromyosin are subunits of myosin filaments (thick myofilaments).