TnI - Troponin I (Human Cardiac Muscle)

General Product Information

The troponin isoforms are prepared from either human cardiac muscle, human skeletal muscle, or rabbit skeletal muscle. Rabbit TnC is supplied as a liquid in 10mM Sodium Phosphate, 150mM Sodium Chloride, pH 7.2 ± 0.1. The protein concentration of Rabbit TnC is determined by A280 using an extinction coefficient of 0.159 (Emg/ml = 0.159). Human TnC is supplied in the same buffer at pH 7.4 ± 0.1 containing 0.02% Azide.

Human TnI (cardiac and skeletal muscle) are both supplied as a liquid in 75mM Tris, 10mM EGTA, 8M Urea, 60mM β-mercaptoethanol, 1mM Calcium Chloride, 1mM Benzamidine, pH 8.0 ± 0.1

Human TnT is supplied as a powder, lyophilized from 10mM HCl. Protein concentration is determined prior to lyophilization by A280 using an extinction coefficient of 0.52 (Emg/ml = 0.52)

TnI+C is prepared in-vitro using human cardiac TnI and rabbit skeletal TnC. It is supplied as a liquid in 50mM Tris, 6M Urea, 3mM Calcium Chloride, 1mM Dithiothreitol, pH 7.8 ± 0.1. DTT is added as a stabilizing agent.

The troponin complex of cardiac and skeletal muscle is a group of contractile proteins composed of three non-identical subunits. Troponin C (TnC) is the calcium sensitive subunit and contains four Ca+2  binding sites. Troponin I (TnI), the inhibitory subunit, binds actin in the relaxed state, thereby preventing muscle contraction by inhibiting the ATPase activity of actomyosin. Troponin T (TnT) is involved in the attachment of the troponin complex to the thin filament, binding tropomyosin and actin. The binding of intracellular Ca+2 by TnC induces a conformational change in the troponin complex, which causes TnI to release actin, subsequently allowing actin to interact with myosin, resulting in muscle contraction. Each subunit of the troponin complex exists in various isoforms depending on its tissue origin.

TnC exists in cardiac, fast-twitch skeletal muscle, and slow-twitch skeletal muscle isoforms, but the slow-twitch and cardiac isoforms are thought to be identical. TnI exists in distinct cardiac, fast-twitch skeletal muscle, and slow-twitch skeletal muscle isoforms. The cardiac isoform is approximately 40% dissimilar from the skeletal muscle isoforms and, in addition, contains 31 N-terminal amino acids not found in the skeletal muscle isoforms.

Elevated serum levels of the cardiac isoforms of the troponin subunits are well-documented in myocardial infarction (MI). Evidence suggests that the subunits exist as the binary Troponin IC complex and as the complete Troponin ICT complex in the serum of MI patients. As such, immunoassays specific for cardiac isoforms must detect these complexes.

Several clinical studies indicate that immunoassays for TnI and TnT are more specific for MI than those for creatine kinase MB isoenzyme. In additions, immunoassays for TnI and TnT are proving useful in the risk stratification of suspected MI patients and in detecting perioperative MI associated with various surgical procedures.

Note: Monoclonal Antibodies are available for Troponin I