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Harper's Illustrated Biochemistry, 28e
Changes in the Conformation of the Head of Myosin Drive Muscle Contraction
Sections: Tropomyosin & the Troponin Complex Present in Thin Filaments Perform Key Functions in Striated Muscle, Ca2+ Plays a Central Role in Regulation of Muscle Contraction, Actin-Based Regulation Occurs in Striated Muscle, The Sarcoplasmic Reticulum Regulates Intracellular Levels of Ca2+ in Skeletal Muscle, Mutations in the Gene Encoding the Ca2+ Release Channel Are One Cause of Human Malignant Hyperthermia.
Topics Discussed: cytoskeleton; excitation-contraction coupling; malignant hyperthermia due to anesthesia; muscle; muscle contraction; ryanodine receptor calcium release channel.
Excerpt:
"How can hydrolysis of ATP produce macroscopic movement? Muscle contraction essentially consists of the cyclic attachment and detachment of the S-1 head of myosin to the F-actin filaments. This process can also be referred to as the making and breaking of crossbridges. The attachment of actin to myosin is followed by conformational changes which are of particular importance in the S-1 head and are dependent upon which nucleotide is present (ADP or ATP). These changes result in the power stroke, which drives movement of actin filaments past myosin filaments. The energy for the power stroke is ultimately supplied by ATP, which is hydrolyzed to ADP and Pi. However, the power stroke itself occurs as a result of conformational changes in the myosin head when ADP leaves it.In striated muscle, there are two other proteins that are minor in terms of their mass but important in terms of their function. Tropomyosin is a fibrous molecule that consists of two chains, alpha and beta, that attach to F-actin in the groove between its filaments (Figure 49–3). Tropomyosin is present in all muscular and muscle-like structures. The troponin complex is unique to striated muscle and consists..."
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