Fast skeletal muscle skinned fibers and myofibrils reconstituted with N-terminal fluorescent analogues of troponin C

H. G. Zot, K. Guth, J. D. Potter

Research output: Contribution to journalArticle

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Abstract

Glycerinated rabbit fast skeletal muscle fibers were chemically skinned with 1% Brij 35 and partially depleted of endogenous troponin C subunit (TnC) by exposure of the fibers to EDTA. The TnC-depleted fibers exhibited a decrease in maximal tension that was mostly restored by readdition of TnC or by the addition of the fluorescent 5-dimethylaminonaphthalene-1-sulfonyl aziridine analogue, TnC(Danz). TnC(Danz) is known to undergo an increase in fluorescence intensity when Ca2+ binds to the two low affinity Ca2+-specific regulatory sites of TnC. Steady-state fractional fluorescence and tension changes were measured simultaneously as a function of Ca2+. The Ca2+ sensitivity of the fluorescence curve was about 0.6 log unit greater than the tension curve. This difference in sensitivity could be explained if separate conformational states of TnC, brought about by Ca2+ binding to the Ca2+-specific sites, produce the fluorescence and tension changes. TnC-depleted fibers were also reconstituted with the fluorescent 2-[(4'-iodoacetamido)analino] naphthalene-6-sulfonic acid analogue, cardiac TnC(Iaans), which undergoes an increase in fluoresence intensity when Ca2+ binds to the single Ca2+-specific regulatory site. The steady-state fractional fluorescence and tension curves for fibers reconstituted with cardiac TnC(Iaans) had nearly the same Ca2+ sensitivity. The steady-state fractional fluorescence of myofibrils reconstituted with TnC(Danz) was found to have a greater sensitivity to Ca2+ than the simultaneously measured ATPase. In all cases paired fractional fluorescence and activity curves tended to have parallel dependence on Ca2+. These procedures make it possible to study the Ca2+ binding properties of the Ca2+-specific sites in intact myofibrils and skinned fibers; the results presented suggest that the Ca2+ affinity of the Ca2+-specific sites of troponin are reduced in the thin filament compared to that of troponin in solution.

Original languageEnglish
Pages (from-to)15883-15890
Number of pages8
JournalJournal of Biological Chemistry
Volume261
Issue number34
StatePublished - Dec 1 1986
Externally publishedYes

Fingerprint

Troponin C
Myofibrils
Skeletal Muscle Fibers
Muscle
Fibers
Fluorescence
Troponin
Sulfonic Acids
Edetic Acid
Adenosine Triphosphatases

ASJC Scopus subject areas

  • Biochemistry

Cite this

Fast skeletal muscle skinned fibers and myofibrils reconstituted with N-terminal fluorescent analogues of troponin C. / Zot, H. G.; Guth, K.; Potter, J. D.

In: Journal of Biological Chemistry, Vol. 261, No. 34, 01.12.1986, p. 15883-15890.

Research output: Contribution to journalArticle

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abstract = "Glycerinated rabbit fast skeletal muscle fibers were chemically skinned with 1{\%} Brij 35 and partially depleted of endogenous troponin C subunit (TnC) by exposure of the fibers to EDTA. The TnC-depleted fibers exhibited a decrease in maximal tension that was mostly restored by readdition of TnC or by the addition of the fluorescent 5-dimethylaminonaphthalene-1-sulfonyl aziridine analogue, TnC(Danz). TnC(Danz) is known to undergo an increase in fluorescence intensity when Ca2+ binds to the two low affinity Ca2+-specific regulatory sites of TnC. Steady-state fractional fluorescence and tension changes were measured simultaneously as a function of Ca2+. The Ca2+ sensitivity of the fluorescence curve was about 0.6 log unit greater than the tension curve. This difference in sensitivity could be explained if separate conformational states of TnC, brought about by Ca2+ binding to the Ca2+-specific sites, produce the fluorescence and tension changes. TnC-depleted fibers were also reconstituted with the fluorescent 2-[(4'-iodoacetamido)analino] naphthalene-6-sulfonic acid analogue, cardiac TnC(Iaans), which undergoes an increase in fluoresence intensity when Ca2+ binds to the single Ca2+-specific regulatory site. The steady-state fractional fluorescence and tension curves for fibers reconstituted with cardiac TnC(Iaans) had nearly the same Ca2+ sensitivity. The steady-state fractional fluorescence of myofibrils reconstituted with TnC(Danz) was found to have a greater sensitivity to Ca2+ than the simultaneously measured ATPase. In all cases paired fractional fluorescence and activity curves tended to have parallel dependence on Ca2+. These procedures make it possible to study the Ca2+ binding properties of the Ca2+-specific sites in intact myofibrils and skinned fibers; the results presented suggest that the Ca2+ affinity of the Ca2+-specific sites of troponin are reduced in the thin filament compared to that of troponin in solution.",
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