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Effects of alkali ions on myosin conformation
Author(s) -
Cheung Herbert C.,
Cooke Roger
Publication year - 1971
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360100308
Subject(s) - chemistry , myosin , spin label , alkali metal , electron paramagnetic resonance , fluorescence , rotational correlation time , ion , crystallography , molecule , solvent , inorganic chemistry , nuclear magnetic resonance , organic chemistry , biochemistry , membrane , physics , quantum mechanics
We have used two probes to study the effects of alkali ions on the conformation of myosin. One was paramagnetic, the “spin label” N ‐(1‐oxyl‐2,2,6,6‐tetramethyl‐4‐piperidinyl)‐maleimide, which binds primarily to SH groups; and the other was fluorescent, l‐anilino‐8‐naphthalenesulfonate, which binds to an apolar niche. The bonding of the spin label to myosin was carried out in 0.6 M LiCl, 0.6 M NaCl, or 0.6 M KCl, and the resulting labeled myosin was studied in the same medium in which the myosin was labeled as well as in other alkali chlorides. The electron paramagnetic resonance spectra of the spin label showed that the structure of myosin in the vicinity of the labeled groups differed in the various salts. The protein surface in the region of the labeled groups restricted the rotational freedom of the spin label more in KCl than in any of the other salts. Although ions are known to influence the properties of myosin, our results show that these ions also effect the molecular structure. The fluorescence of l‐anilino‐8‐naphthalenesulfonate, noncovalently attached to myosin in the presence of alkali chlorides, decreased progressively with increasing size of the cations, again showing the protein structure near the probe attachment to be a function of the cation, in the solvent. Ca 2+ quenched the fluorescence of the bound probe, indicating an interaction between Ca 2+ and the myosin molecule. The effect of Ca 2+ on the fluorescence was greatest in KCl.