Titin: "a third filament system of the sarcomere" (Labeit, Kolmerer, & Linke, 1997, p. 290)

Strands of titin, a large protein molecule, extend from each sarcomere's Z discs to its M-lines, and anchor the myosin molecules that participate in the production of active force.

Titin, therefore, maintains the proximity of actin and myosin for active force production, and also contributes to the muscle's passive-elastic properties. The schematic diagram of titin to the right is from Scott (2000)

References:

Labeit, S., Kolmerer, B., & Linke, W.A. (1997). The giant protein titin. Emerging roles in physiology and pathophysiology. Circulation Research, 80, 290-4.

Lieber, R.L., & Bodine-Fowler, S.C. (1993). Skeletal muscle mechanics: Implications for rehabilitation. Physical Therapy, 73, 844-856.

Scott, K. (2000). What is titin? Cambridge, UK, Cambridge University, Department of Chemistry. Retrieved January 17, 2001, from the World Wide Web: http://chemsoc.com/exemplarchem/entries/kscott/titin.htm

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