Among the key proteins involved in muscle contraction, troponin is the muscle protein with the affinity to bind calcium ions (Ca++). This binding plays a fundamental role in the regulation of contraction in striated muscles, including skeletal and cardiac muscles.

Role of Troponin in Calcium Binding and Muscle Contraction

Troponin is a complex of three subunits — troponin C, troponin I, and troponin T — associated with the thin filaments of muscle fibers. The subunit troponin C specifically binds calcium ions released during muscle excitation.

When calcium ions bind to troponin C, it induces conformational changes in the troponin complex, which leads to the movement of tropomyosin away from the myosin-binding sites on actin filaments. This exposure allows myosin heads to attach to actin, initiating cross-bridge cycling and muscle contraction.

Other Muscle Proteins and Calcium

• Tropomyosin lies along the actin filaments and blocks myosin binding sites during rest but does not itself bind calcium.

• Actin is the major filamentous protein forming thin filaments but does not have a calcium-binding role.

• Myosin forms thick filaments and functions as a motor protein using ATP hydrolysis; it does not bind calcium ions for regulation.

Conclusion

Therefore, the muscle protein with affinity to bind Ca++ ions is:

(2) Troponin