Troponin I is a subunit of the troponin complex (Tn), which is a heteromeric protein that is bound to the thin filament. The troponin complex plays an important role in the regulation of skeletal and cardiac muscle contraction. The complex consists of three subunits: troponin T (TnT), troponin I (TnI) and troponin C (TnC). These subunits are held together by non-covalent interactions. TnT is the tropomyosin-binding subunit that regulates interaction between the troponin complex and the thin filament. The TnI subunit is responsible for inhibiting actomyosin formation at low intracellular Ca2+ concentrations. The TnC subunit binds Ca2+ ions during the excitation of the muscle and changes the conformation of the troponin complex, thus enabling the formation of actomyosin complex and the subsequent muscle contraction (1).