Which of the following is called a 'relaxation protein'?
Actin
Myosin
Tropomyosin
Dystrophin
Troponin tropomyosin complex are called relaxation proteins and is found to inhibit the interaction between actin and myosin thereby preventing cross bridge formation. During resting stage troponin I is lightly bound to actin and the tropomyosin molecules are located in the groove between the strands of actin filaments in such a way that they block the myosin binding sites on actin. When activation occurs, calcium released into the sarcoplasmic reticulum gets attached to the troponin C subunit of troponin. This in turn cause a conformational change which cause the tropomyosin molecule to move laterally uncovering the binding sites on the actin filament for the head of myosin molecules. Ref: Essentials Of Medical Physiology By Khurana, page 51