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Mobile segments in rabbit skeletal muscle F‐actin detected by 1 H nuclear magnetic resonance spectroscopy
Author(s) -
Ślósarek Genowefa,
Heintz Daniela,
Kalbitzer Hans Robert
Publication year - 1994
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(94)00894-9
Subject(s) - actin , quenching (fluorescence) , chemistry , ionic strength , nuclear magnetic resonance spectroscopy , excited state , ion , phalloidin , polymerization , crystallography , analytical chemistry (journal) , stereochemistry , atomic physics , polymer , cytoskeleton , fluorescence , biochemistry , physics , chromatography , organic chemistry , quantum mechanics , aqueous solution , cell
Polymerization of actin by increasing the ionic strength leads to a quenching of almost all 1 H NMR signals. Surprisingly, distinct signals with relatively small line widths can still be observed in actin filaments (F‐actin) indicating the existence of mobile, NMR visible residues in the macromolecular structure. The intensity of the F‐actin spectrum is much reduced if one replaces Mg 2+ with Ca 2+ , and a moderate reduction of the signal intensity can also be obtained by increasing the ionic strength. These results can be explained in a two‐state model of the actin protomers with a M‐ (mobile) state and a I‐ (immobile) state in equilibrium. In the M‐state a number of residues in the actin protomer are mobile and give rise to observable NMR signals. This equilibrium is shifted towards the I‐state specifically by replacing Mg 2+ with Ca 2+ ‐ions and unspecifically by addition of monovalent ions such as K + . The binding of phalloidin to its high‐affinity site in the filaments does not influence the equilibrium between M‐ and I‐state. Phalloidin itself is completely immobilized in F‐actin, its exchange with the solvent being slow on the NMR time scale.