. Explain the term Molecular Mechanism of Muscle Contraction


Best Answer

Molecular Mechanism of Muscle Contraction

The mass of a fresh muscle is made up of 75% water and more than 20% protein. The two major proteins are actin and myosin.

Monomeric G-actin makes up 25% of muscle protein by weight. At physiologic ionic strength and in the presence of Mg2+, G-actin polymerizes noncovalently to form an insoluble double helical filament called F-actin.

Myosin contributes 55% of muscle protein by weight and forms the thick filaments. It is an asymmetric hexamer. Myosin has a fibrous tail consisting of two intertwined helices. Each helix has a globular head portion attached at one end. The hexamer consists of one pair of heavy (H) chains and two pairs of light (L) chains.

When myosin is digested with trypsin, two myosin fragments (meromyosins) are generated. Light meromyosin (LMM) consists of aggregated, insoluble  -helical fibers from the tail of myosin. LMM exhibits no ATPase activity and does not bind to F-actin.

Heavy meromyosin is a soluble protein that has both a fibrous portion and a globular portion. It exhibits ATPase activity and binds to F-actin.

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