Is troponin a protein or an enzyme?

From the Guidelines

Troponin is a protein, not an enzyme, and it plays a crucial role in muscle contraction by regulating the interaction between actin and myosin filaments in muscle tissue. The most recent and highest quality study, 1, published in the Journal of the American College of Cardiology in 2000, supports this definition of troponin. According to this study, troponin is a complex of three proteins (troponin C, troponin I, and troponin T) found in cardiac and skeletal muscle.

Key Characteristics of Troponin

• Troponin is a biomarker for heart damage, and when heart muscle cells are injured, it is released into the bloodstream.
• Elevated blood levels of cardiac troponin (particularly troponin I and troponin T) are highly specific indicators of myocardial injury.
• Troponin's function is structural and regulatory within muscle tissue, unlike enzymes, which catalyze biochemical reactions.
• The 99th percentile of a reference control group is used to define an increased value for cardiac troponin, as stated in 1 and 1.

Clinical Significance of Troponin

• Troponin tests are essential in diagnosing heart attacks and other cardiac conditions.
• The degree of biomarker elevation is related to clinical risk, and the classification for the extent of myocardial damage is based on the level of troponin elevation, as mentioned in 1.
• Troponin values may remain elevated for 7 to 10 days or longer after myocardial necrosis, and care should be exercised in attribution of elevated cardiac troponin levels to very recent clinical events, as noted in 1.

Comparison with Other Biomarkers

• Cardiac troponin is preferred over CK-MB and total CK due to its high sensitivity and specificity for myocardial damage, as stated in 1.
• CK-MB is less tissue-specific than cardiac troponin but has more robust data documenting its clinical specificity for irreversible injury, as mentioned in 1.
• Total CK is not recommended for the routine diagnosis of acute MI due to its wide tissue distribution, as noted in 1.

From the Research

Definition of Troponin

• Troponin is a component of skeletal and cardiac muscle thin filaments, consisting of three subunits - troponin I, T, and C 2.
• It plays a crucial role in muscle activity, connecting changes in intracellular Ca2+ concentration with generation of contraction 2.
• Troponin is described as a molecular switch, directly regulating the Ca2+-dependent activation of myofilament in striated muscle contraction 3.

Classification of Troponin

• Troponin is classified as a protein, being a component of the contractile mechanism of muscle, including cardiac muscle 4.
• It is not classified as an enzyme, as there is no evidence in the provided studies to suggest that it has enzymatic activity 2, 3, 5, 6, 4.

Functions and Applications of Troponin

• Troponin is utilized in medicine as a target for some cardiotonic drugs used in the treatment of heart failure 2.
• Cardiac isoforms of troponin I and T have been widely used for immunochemical diagnostics of pathologies associated with cardiomyocyte death (myocardial infarction, myocardial trauma, and others) 2.
• Troponin measurements are highly sensitive and specific for the early and late diagnosis of myocardial damage 6.