A TROPONIN complex subunit that inhibits ACTOMYOSIN ATPASE activity thereby disrupting ACTIN and MYOSIN interaction. There are three troponin I subtypes: troponin I1, I2 and I3. Troponin I3 is cardiac-specific whereas troponin I1 and I2 are skeletal subtypes. Troponin I3 is a BIOMARKER for damaged or injured CARDIAC MYOCYTES and mutations in troponin I3 gene are associated with FAMILIAL HYPERTROPHIC CARDIOMYOPATHY.

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. In the absence of calcium, Troponin I binds actin, inhibits actomyosin ATPase activity, and inhibits F-actin-myosin interactions. The troponin I gene family comprises three isoforms: skeletal TNI-fast, skeletal TNI-slow, and TNI-cardiac. (from OMIM 191044, 191043, 191042 and NCI)