Myofilament is the term for the chains of (primarily) actin and myosin that pack a muscle fiber. These are the force generating structures.
Although there are still gaps in what we know of the structure and functional significance of the myofilament lattice, some of the key proteins include:
This peptide is responsible for force generation. It is composed of a globular head with both ATP and actin binding sites, and a long tail involved in its polymerization into myosin filaments.
The other major component in force production. Actin, when polymerized into filaments, forms the "ladder" along which the myosin filaments "climb" to generate motion.
Apparently the major regulator of force production. Its three subunits lie in the groove of each actin filament blocking the myosin binding site, in the absence of ionic calcium.
An enormous (2500 kD) peptide that appears to be involve in maintaining the neatly ordered striation pattern. Closely associated with the myosin molecule, it appears to anchor the myosin network to the actin network.
Another actin associated molcule, nebulin appears to act as a molecular ruler regulating the length of actin filaments.
In cross section, under very high magnification, both A and I bands can be seen to be hexagonal networks. These networks are apparently ordered and fixed at the M- and Z-lines. In the region where the A and I bands overlap (sometimes known as the H band) the two hexagonal networks intermesh so that each myosin filament is surrounded by six actin filaments.
These networks appear to be anchored to (and through) the cell membrane in two ways. At the ends of fibrils, special structures anchor the terminal actin filaments to the membrane. There also appear to be connections between the Z and M lines and the cell membrane.
Last Updated: Friday, 13-Jan-2006 15:56:17 PST
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