The complex protein distributed at regular intervals on the tropomyosin is 

The complex protein distributed at regular intervals on the tropomyosin is  troponin. Troponin plays a crucial role in regulating muscle contraction. It consists of three subunits: troponin I (TnI), troponin T (TnT), and troponin C (TnC).

• Troponin I (TnI) inhibits muscle contraction by binding to actin and preventing the interaction between actin and myosin when the muscle is at rest.
• Troponin T (TnT) binds to tropomyosin and anchors the troponin complex to the actin filament.
• Calcium ions (Ca²⁺) bind to troponin C (TnC). When calcium levels increase in response to a nerve signal, it binds to TnC, causing a conformational change in the troponin complex. This conformational change leads to the movement of tropomyosin away from the active sites on actin, allowing myosin heads to bind to actin and initiate muscle contraction.