Troponin is a complex of proteins found in cardiac and skeletal muscles that plays a crucial role in muscle contraction. It consists of three subunits: troponin C, troponin I, and troponin T, which work together to regulate the interaction of actin and myosin in muscle fibers. Troponin levels are often measured in clinical settings to diagnose heart conditions, as elevated levels can indicate cardiac muscle damage, such as in myocardial infarction.