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  • Title: Utilization of troponin C as a model calcium-binding protein for mapping of the calmodulin-binding sites of caldesmon.
    Author: Polyakov AA, Gusev NB.
    Journal: Biochem J; 1997 Feb 01; 321 ( Pt 3)(Pt 3):873-8. PubMed ID: 9032478.
    Abstract:
    Troponin C, a structural analogue of calmodulin, was used for mapping the calmodulin-binding sites of caldesmon. The apparent Kd values for the formation of the caldesmon-calcium-binding-protein complex as determined by native gel electrophoresis were 0.5, 1.2 and 3.9 microM for calmodulin, rabbit skeletal muscle troponin C and bovine cardiac troponin C respectively. Troponin C induced a 4-6 nm blue shift of the Trp fluorescence of caldesmon without affecting the amplitude of fluorescence. In the presence of Ca2+, troponin C induced partial displacement of caldesmon from actin tropomyosin complexes. Addition of 5,5'-dithiobis(nitrobenzoic) acid to an equimolar complex of caldesmon and troponin C induced disulphide cross-linking between Cys-98 of rabbit skeletal muscle troponin C and the single Cys residue of duck gizzard caldesmon, located in a position analogous to Cys-580 of the chicken gizzard protein. The cross-linked caldesmon-troponin C complex was ineffective in inhibiting actomyosin ATPase activity. It is concluded that Cys-580 of caldesmon can be located close to both the central helix of calcium-binding proteins and the C-terminal domain of actin. This may be important for the regulation of actomyosin ATPase activity by caldesmon.
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