[Troponin I, troponin T, and troponin C are the three closely associated subunits of the troponin complex of thin filaments in muscle. The complex serves as a calcium-sensitive switch that regulates muscle contraction. Because it is not normally found in blood, cardiac troponin-T in serum is a sensitive indicator of myocardial cell injury. ( NCI )] (UMLS (CSP) C0077404) =Amino Acid, Peptide, or Protein; Biologically Active Substance ;