title: Millisecond photo-cross-linking of protein components in vertebrate striated muscle thin filaments.
abstract: Troponin I (TnI) was reacted with a photosensitive heterobifunctional reagent, methyl 4-azidobenzimidate (ABI), and then troponin was reconstituted with the ABI-modified TnI. Flash irradiation of the reconstituted troponin resulted in the formation of cross-links between TnI and other components of troponin, troponin C (TnC) and troponin T (TnT), suggesting that TnI is in contact with TnC and TnT when troponin is free in solution. No effect of calcium on the cross-linking could be detected. When the reconstituted troponin was complexed with F-actin-tropomyosin, flash irradiation of the reconstituted then filament yielded the cross-linked products of TnC-TnI, TnI-TnT, and TnI-actin in the presence ans absence of calcium, indicating that TnI is in contact with TnC, TnT, and actin in the thin filament complex irrespective of calcium concentration. No cross-linking could be detected between TnI and tropomyosin. Calcium was found to affect the cross-linking of TnC-TnI and TnI-actin; when TnC was saturated with calcium, the extent of the TnC-TnI cross-linking increased, while that of the TnI-actin cross-linking decreased. Calcium did not affect the TnI-TnT cross-linking.
mesh_terms: D000199:Actins / Q000378:metabolism; D000251:Adenosine Triphosphatases / Q000378:metabolism; D001386:Azides; D002118:Calcium / Q000494:pharmacology; D003432:Cross-Linking Reagents; D004533:Egtazic Acid / Q000494:pharmacology; D007096:Imidoesters; D008970:Molecular Weight; D009124:Muscle Proteins / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D014335:Tropomyosin / Q000378:metabolism; D014336:Troponin / Q000378:metabolism*
chemical_list: D000199:Actins; D001386:Azides; D003432:Cross-Linking Reagents; D007096:Imidoesters; D009124:Muscle Proteins; D014335:Tropomyosin; D014336:Troponin; D004533:Egtazic Acid; C026810:methyl 4-azidobenzimidate; D000251:Adenosine Triphosphatases; D002118:Calcium