The interaction between beef cardiac troponin T and troponin I as demonstrated by ultraviolet absorption difference spectroscopy, circular dichroism, and gel filtration.

The specific interaction of bovine cardiac troponin T with troponin I has been demonstrated at a 1:1 molar ratio by absorption difference spectroscopy, near and far ultraviolet circular dichroism, and gel filtration chromatography. The maintenance of the sulfhydryl groups of both proteins in the reduced state was essential in order to demonstrate interaction between cardiac troponin I and troponin T using the aforementioned methodology. Carboxamido-methylated troponin I and troponin T samples were prepared by reaction with iodoacetamide. Spectrophotometric titration of the two proteins with 2-chloromercurinitrophenol and amino acid analysis of their carboxamidomethylated derivatives revealed that cardiac troponin I possesses two cysteine residues while cardiac troponin T has one. The modified troponin T possesses properties identical to those of the native molecule. The modification of troponin I is accompanied by an increase in secondary structure and a loss in ability to interact with troponin T at 0.5 M NaCl ionic strength. However, at 0.3 M NaCl the modified troponin I was shown by gel filtration chromoatography to interact very weakly with troponin T. On the other hand, the modified troponin I interacts with troponin C in a manner identical to the native protein, indicating that the troponin T interaction domain of the molecule is distinct from that region which interacts with troponin C.