Cardiac troponin is composed of three subunits, namely cardiac troponin T (cTnT), cardiac troponin I (cTnI), and cardiac troponin C (cTnC).They collectively participate in the regulation of cardiac muscle contraction. The amino-terminal and carboxyl-terminal ends of cTnImolecules are prone to degradation through protein hydrolysis. Cardiac troponin I (cTnI) is an important regulatory factor that inhibits musclecontraction under normal circumstances. It binds to actin, preventing the interaction between actin and cardiac troponin C (cTnC), thusinhibiting muscle contraction. The phosphorylation status of cTnI can alter its affinity for actin, thereby influencing the regulation of musclecontraction. The serine residues at positions 22 and 23 of cTnI are susceptible to phosphorylation by protein kinase A, which regulatesmuscle contraction. Abnormal levels of phosphorylation may also contribute to muscle dysfunction or the development of heart disease.
