Actin&;s active site is covered by

Tropomyosin molecules are long filaments located in the groove between the two chains in the action. In resting muscle, troponin I is bound to actin and tropomyosin and covers the sites wheremyosin heads interact with actin. The thick filaments, which are about twice the diameter of the thin filaments, are made up of myosin. Troponin is Ca2+-binding protein involved in contraction of skeletal muscle. Additional structural proteins that are impoant in skeletal muscle function include desmin. Desmin adds structure to the Z lines in pa by binding the Z lines to the plasma membrane(REF.GANONG'S REVIEW OF MEDICAL PHYSIOLOGY -23rd EDITION. Page No-94,96)