Purification and characterization of troponin C from pike muscle: a comparative spectroscopic study with rabbit skeletal muscle troponin C.

The conformation of troponin C (TN-C) isolated from the white muscle of pike (Esox lucius), in the Ca2+ and metal-free states, was studied by circular dichroism, absorption difference spectroscopy, solvent perturbation difference spectroscopy, intrinsic fluorescence, thiol titration, and 1H nuclear magnetic resonance spectroscopy. In addition, the molecular weight of the protein was determined by sedimentation equilibrium and polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The composition of the protein was established by amino acid analysis. The resulting data were compared with those from the widely studied analogue isolated from rabbit skeletal muscle. The results indicate near equivalence in many of the properties of pike and rabbit TN-C, such as molecular weight, the magnitude of the calcium-induced conformational change, and urea- or thermal-induced denaturability. However, the pike protein has five additional potential carboxyl groups, and there is good evidence from NMR, solvent perturbation, and fluorescence studies for the presence of a buried tyrosine residue in the apo state.