Spectrofluorometric analysis of length-dependent conformational changes in cardiac troponin C

Y. M. Liou, Y. C. Tseng, J. C. Cheng

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1 Citation (Scopus)


Length modulation of cardiac muscle is manifested in the Frank-Starling relation of the heart. Recently, it has been shown that length-dependent changes in SH reactivity of cardiac troponin C (cTnC) occurred in association with cross-bridge attachment and Ca2+. However, the presence of two SH groups (Cys-35 and Cys-84) in the regulatory region of cTnC complicates efforts to detect conformational changes. In this study skinned porcine cardiac fibers were reacted with 7-diethylamino-3-[4′maleimidylphenyl]-4-methylcoumarin (CPM). Alkaline urea gel electrophoresis, along with protein elution, was used to isolate filament bound cTnC. Analysis of fluorescence measurement showed that there is a Ca2--increased fluorescence for CPM-labeled cTnC in long fibers (sarcomere length = 2.2 ∼ 2.5 μm) but not in short fibers (sarcomere length = 1.6 ∼ 1.8 μm). In addition, the labeled cTnC was measured for the fluorescence decrease over time by adding a non-fluorescence energy acceptor, 4-dimethylaminophenylazophenyl-4′maleimide (DABMI), in the presence and absence of Ca2+. Fluorescence quenching by DABMI is not affected by Ca2+ in long fibers but it is significantly increased in short fibers. However, the fibers maintained in the relaxed state with 5 mM MgATP and 1 mM Vanadate showed no length effect on the CPM-labeled cTnC in terms of the Ca2+-mediated changes in fluorescence spectrum and in fluorescence quenching by DABMI. All together, our results suggest that the relative reactivities of Cys-35 and Cys-84 vary with sarcomere length.

Original languageEnglish
Pages (from-to)309-315
Number of pages7
JournalJournal of Muscle Research and Cell Motility
Issue number4
Publication statusPublished - 2002
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Physiology
  • Cell Biology


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