MICROANATOMY

Detailed explanation-1: -Troponin, which regulates the tropomyosin, is activated by calcium, which is kept at extremely low concentrations in the sarcoplasm. If present, calcium ions bind to troponin, causing conformational changes in troponin that allow tropomyosin to move away from the myosin-binding sites on actin.

Detailed explanation-2: -Bottom panel: Calcium (Ca2+) binds to troponin C, leading to a conformational change which moves the tropomyosin molecule and makes the myosin binding site accessible to the myosin head. The other troponins also contribute to this process.

Detailed explanation-3: -Troponin plays a central role in the calcium-regulation of muscle contraction: Troponin is the sole calcium-binding component of thin filaments (actin-tropomyosin-troponin complex) of striated muscles. Thin filaments without troponin support contraction irrespective of calcium concentration.

Detailed explanation-4: -Troponin complex comprises three polypeptides (E1, P5): 1. TnT (molecular mass of 37 kDa) has a binding site for tropomyosin and is thought to be responsible for binding the troponin complex to tropomyosin (R1).