Troponin Iis a cardiac and skeletal muscle protein useful in the laboratory diagnosis of heart attack. It occurs in different plasma concentration but the same circumstances as troponin T - either test can be performed for confirmation of cardiac muscle damage and laboratories usually offer one test or the other.
Troponin I is a part of the troponin protein complex, where it binds to actin in thin myofilaments to hold the actin-tropomyosin complex in place. Because of it, myosin cannot bind actin in relaxed muscle. When calcium binds to the troponin C it causes conformational changes which lead to dislocation of troponin I and finally tropomyosin leaves the binding site for myosin on actin leading to contraction of muscle.
It is considered to be more sensitive and significantly more specific in diagnosis of the myocardial infarction than the "golden marker" of last decades –CK-MB, as well as total creatine kinase, myoglobinand lactate dehydrogenase isoenzymes.