<prompt> Why is Troponin C not used for MI diagnosis?Ttroponin C binds to calciumTroponin C is present in both cardiac and smooth muscleTroponin C is present in both cardiac and skeletal muscleIt elevates late after onset of MI.  <response>: Ans. b troponin C is present in both cardiac and smooth muscleRef: Harrison 19th ed. 265e-7 Troponins of cardiac origin are regulatory proteins that control the calcium mediated interaction of Actin and Myosin. The troponin complex consists of three subunits: Troponin T, which binds to Tropomyosin and facilitates contractions; Troponin I, which binds to Actin and inhibits ActinMyosin interaction; and Troponin C, which binds the calcium ions The amino acid sequence of the skeletal and cardiac isoforms of Troponin T and Troponin I are sufficiently dissimilar and therefore detectable by monoclonal antibody assay. Troponin C is not used clinically because both cardiac and smooth muscle share Troponin C isoforms 