Absorption, fluorescence, and linear dichroism spectra of fluorescein mercuric acetate (FMA) bound to F-actin. Two kinds of effects of divalent cations.
Two kinds of F-actin were prepared; one binds magnesium at the unique divalent cation binding site of actin protomer and the other binds calcium at this site. They were designated as F(Mg)-actin and F(Ca)-actin, respectively. The binding of fluorescein mercuric acetate (FMA) to F(Mg)-actin and F(Ca)-actin was studied spectroscopically. The absorption and fluorescence spectra of bound FMA differed slightly but distinctly between F(Mg)-actin and F(Ca)-actin. Moreover, FMA bound to F(Mg)-actin showed linear dichroism in the presence of 2 mM MgCl2 (or 2mM CaCl2) in the solvent, while the dichroism was abolished by the removal of divalent cations from the solvent. In contrast, FMA bound to F(Ca)-actin did not show any appreciable linear dichroism irrespective of the presence (or absence) of divalent cations in the solvent. These results suggest that the structure of F-actin is characteristically regulated by divalent cations in a dual mode.
D000199:Actins; D000818:Animals; D005033:Ethylmaleimide; D005452:Fluoresceins; D007700:Kinetics; D009132:Muscles; D009941:Organomercury Compounds; D011487:Protein Conformation; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry
D000199:Actins; D005452:Fluoresceins; D009941:Organomercury Compounds; D005033:Ethylmaleimide