Document Detail

Osmotic properties of the calcium-regulated actin filament.
MedLine Citation:
PMID:  7827025     Owner:  NLM     Status:  MEDLINE    
The diameter of the actin filament decreases with an increase of the protein osmotic pressure. This phenomenon is accompanied by a decrease of the angle (alpha) formed between the long axis of the actin monomer and the pointed end of the filament axis. At 1.8 x 10(5) dyn/cm2 (the protein osmotic pressure in frog muscle) the diameter is 8.34 nm and the angle (alpha) is 61.5 degrees. The interfilament distance of tropomyosin-decorated actin filaments, at a set of different osmotic pressures, is larger than that of F-actin filaments. This suggests that the two tropomyosin helices project out of the contour of the actin filament. The tropomyosin-decorated actin filament is more rigid than F-actin. At 1.8 x 10(5) dyn/cm2, the angle (alpha) is 76.4 degrees, as compared to the value of 61.5 degrees for F-actin. The interfilament distance of troponin-tropomyosin-decorated actin filaments is sensitive to Ca2+: in the physiological range of protein osmotic pressure it decreases from 13.3 nm, in the presence of 2 mM EGTA, to 12.2 nm in the presence of 0.2 mM CaCl2. Two alternative models are proposed to explain the decrease in interfilament distance. (a) Calcium shifts tropomyosin along the actin monomer, toward the filament axis (the classical model). (b) Calcium releases the rigidity of the tropomyosin-decorated filament and restores the original plasticity of F-actin. The consequent decrease of the angle (alpha) brings the tropomyosin helices nearer to the filament axis, without any real movement of tropomyosin along the actin monomer.
C Schwienbacher; E Magri; G Trombetta; E Grazi
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Publication Detail:
Type:  In Vitro; Journal Article; Research Support, Non-U.S. Gov't    
Journal Detail:
Title:  Biochemistry     Volume:  34     ISSN:  0006-2960     ISO Abbreviation:  Biochemistry     Publication Date:  1995 Jan 
Date Detail:
Created Date:  1995-02-23     Completed Date:  1995-02-23     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  0370623     Medline TA:  Biochemistry     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1090-5     Citation Subset:  IM    
Dipartimento di Biochimica e Biologia Molecolare, Università di Ferrara, Italy.
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MeSH Terms
Actins / chemistry*
Biophysical Phenomena
Calcium / chemistry
Microfilaments / chemistry,  ultrastructure*
Muscle Contraction*
Tropomyosin / chemistry
Water-Electrolyte Balance*
Reg. No./Substance:
0/Actins; 0/Tropomyosin; 7440-70-2/Calcium

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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