title: Hydrodynamic properties of bovine cardiac troponin-I and troponin-T.
abstract: Bovine cardiac troponin-I (TN-I) and troponin-T (TN-T) have been examined in solution using ultracentrifugation, gel filtration, and viscosity. A new method of purifying TN-T, employing hydroxylapatite chromatography in 6 M urea, is reported. Cardiac TN-T (Mr = 36,000) undergoes a reversible, concentration-dependent association in nondenaturing buffers, probably to a tetramer. The Stokes radius (Rs) of aggregated TN-T, determined by sedimentation velocity and gel chromatography on Sephacryl S-300, is 80 A and the reduced viscosity of the subunit ranges from 20 to 25 ml/g at protein concentrations between 0.5 and 2.5 mg/ml. These data suggest that TN-T forms highly asymmetric aggregates in solution. Bovine cardiac TN-I also has a tendency toward self-association, but is essentially monomeric (Mr = 23,000) at protein concentrations below 1 mg/ml. The presence of reducing agent is necessary to avoid intermolecular disulfide bond formation. From gel filtration experiments, the value of Rs is 29 A indicating that TN-I is a moderately asymmetric protein (frictional ratio = 1.5). Similar properties are observed when both sulfhydryl groups of TN-I are modified by carboxamidomethylation.
mesh_terms: D000818:Animals; D002417:Cattle; D008970:Molecular Weight; D009124:Muscle Proteins / Q000302:isolation & purification; D009206:Myocardium / Q000378:metabolism*; D011487:Protein Conformation; D013438:Sulfhydryl Compounds / Q000032:analysis; D014336:Troponin / Q000302:isolation & purification; D019210:Troponin I; D020107:Troponin T; D014461:Ultracentrifugation; D014783:Viscosity
chemical_list: D009124:Muscle Proteins; D013438:Sulfhydryl Compounds; D014336:Troponin; D019210:Troponin I; D020107:Troponin T