The interaction of the calcium-binding protein (troponin C) with bivalent cations and the inhibitory protein (troponin I)

Abstract

1. The molecular weight of the calcium-binding protein of rabbit white skeletal muscle was estimated to be 18500 by sedimentation equilibrium and electrophoresis in sodium dodecyl sulphate. 2. Addition of 2 Ca(2+) ions per molecule produced reversible changes in the u.v.-absorption spectrum that are interpreted as arising from conformational changes in the structure of the protein. 3. Cd(2+) was almost as effective as Ca(2+) in producing the spectral changes. Other bivalent metal ions, particularly Mg(2+), were less effective. 4. Binding of Ca(2+) by the calcium-binding protein produced an increase in mobility to the anode on electrophoresis in 6m-urea at pH8.6. The Ca(2+)-saturated form of the protein was more retarded on gel filtration than the Ca(2+)-free form. 5. In the presence of Ca(2+) the calcium-binding protein formed an equimolar complex with the inhibitory protein. This complex was stable in 8m-urea and in the pH range 7.0-8.6. 6. An isotope-dilution method for the measurement of the content of calcium-binding protein in whole muscle is described. In rabbit psoas muscle the ratio of actin monomers to molecules of calcium-binding protein was approx. 7:1. Similar values were obtained for red skeletal and cardiac muscle. 7. Evidence is presented indicating that in the rabbit the inhibitory protein of the troponin complex of red skeletal and cardiac muscles is different from the inhibitory protein of white skeletal muscle.

Cloning and expression of chicken skeletal muscle troponin I in Escherichia coli: The role of rare codons on the expression level

“…TnI binds TnC in urea gels in a calcium-dependent fashion (Head & Perry, 1974). As shown in Figure lC, in the presence of Ca2+, a stable complex between recombinant TnC and recombinant TnI can be observed in polyacrylamide gels containing 6 M urea.…”

Calcium-binding proteins in the vorticellid spasmoneme

“…Troponin C binds calcium in 6 M urea with a small increase in electrophoretic mobility; if, however, the Mg-ATPase inhibitory protein (troponin I) is also present in the calcium-urea gel, the two proteins interact, forming a slower migrating complex (17). Thus, both the calciumbinding site(s) and the troponin I recognition site of the troponin C molecule retain their integrity in 6 M urea.…”

“…Both troponin C and parvalbumin are able to interact with calcium even in the presence of high concentrations of urea (17,35), suggesting that the calcium-protein complex is highly stable and can resist the denaturing effect of strong urea solutions. Troponin C binds calcium in 6 M urea with a small increase in electrophoretic mobility; if, however, the Mg-ATPase inhibitory protein (troponin I) is also present in the calcium-urea gel, the two proteins interact, forming a slower migrating complex (17).…”

“…Urea-polyacrylamide gels were also run on the microslab gel electrophoresis apparatus according to the formula of Head and Perry (17). A discontinuous pH gradient was not used.…”

Phylogenetic diversity of troponin subunit‐C amino acid composition

“…The purity and electrophoretic mobility of the troponins-C were ascertained by SDS-and alkalineurea polyacrylamide gel electrophoresis as in [5] and [6], respectively ( fig.l,2). Amino acid composition of 24 h hydrolysates were determined using a Beckman 119C 1 amino acid analyzer.…”