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Organism of Origin

This protein originated in tarantulas, red junglefowls and humans.

Protein Structure

Heavy meromyosin (HMM) is a subunit of myosin. There are two fragments that make up HMM: S-1 and S-2. S-1 projects out on an angle whereas S-2 is comprised of globular heads that can bind to actin. Together, these are called a myosin cross bridge. There are four distinct macromolecules that comprise HMM, including Myosin II regulatory light chain (196 amino acids: magenta), (150 amino acids: blue), Myosin 11; Myosin 7 (971 amino acids: gold), and Myosin 7; Myosin 11 (973 amino acids: purple).

Function

Heavy meromyosin is a part of the actin-myosin system. Heavy meromyosin (and light meromyosin) are subunits of myosin. HMM is the globular head portion of myosin which determines the rate of muscle contraction in an organism. Actin binding capacity and ATPase activity are dependent on HMM.

Significance

Heavy meromyosin is important for muscle contractions in a multitude of organisms. It plays an important role in microtubule-based movement as a part of the myosin complex. The ability for myosin to bind to actin and use ATP to create mechanical energy is dependent on heavy meromyosin. Without this protein, muscle contraction and mobility would be limited.