Troponin I Degradation and Covalent Complex Formation Accompanies Myocardial Ischemia/Reperfusion Injury

Abstract—Selective troponin I (TnI) modification has been demonstrated to be in part responsible for the contractile dysfunction observed with myocardial ischemia/reperfusion injury. We have isolated and characterized modified TnI products in isolated rat hearts after 0, 15, or 60 minutes of ischemia followed by 45 minutes of reperfusion using affinity chromatography with cardiac troponin C (TnC) and an anti-TnI antibody, immunological mapping, reversed-phase high-performance liquid chromatography, and mass spectrometry. Rat cardiac TnI becomes progressively degraded from 210 amino acid residues to residues 1–193, 63–193, and 73–193 with increased severity of injury. Degradation is accompanied by formation of covalent complexes between TnI 1–193 and, respectively, TnC residues 1–94 and troponin T (TnT) residues 191–298. The covalent complexes are likely a result of isopeptide bond formation between lysine 193 of TnI and glutamine 191 of TnT by the cross-linking enzyme transglutaminase. With severe ischemi...