Open AccessTropomodulin isolated from rabbit skeletal muscle inhibits filament formation of actin in the presence of tropomyosin and troponin
Author(s) -
Kimura Sumiko,
Ichikawa Akira,
Ishizuka Junko,
Ohkouchi Shiho,
Kake Takei,
Maruyama Koscak
Publication year - 1999
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1046/j.1432-1327.1999.00505.x
Subject(s) - tropomyosin , actin , troponin , skeletal muscle , protein filament , chemistry , biophysics , biochemistry , biology , anatomy , medicine , myocardial infarction
Tropomodulin is a tropomyosin‐binding protein, originally isolated from human erythrocytes. Tropomodulin is currently regarded as the sole actin pointed‐end capping protein [Weber, A., Pennise, C.R., Babcock, G.G. & Fowler, V.M. (1994) J. Cell Biol. 127 , 1627–1635]. This work first describes a procedure for the purification of tropomodulin from rabbit skeletal muscle. Tropomodulin almost completely inhibited filament formation of actin in the presence of tropomyosin and troponin. For the maximal inhibition of actin polymerization, ≈ 0.10, 0.12 and 0.003 mol of tropomyosin, troponin and tropomodulin per mol of actin were required, respectively. Fluorescence‐intensity measurements, electron‐microscopy and sedimentation experiments revealed that only very short fragments and amorphous aggregates, but not filaments, were formed when actin was copolymerized with tropomyosin, troponin and tropomodulin by the addition of 50 m m KCl at pH 8.0. The effects of tropomyosin, troponin and tropomodulin were more remarkable on Ca‐actin than on Mg‐actin. It appears that tropomodulin caps both the pointed and barbed ends of tropomyosin‐ and troponin‐bound actin filaments.