title: Evidence that the ATP binding site of sarcoplasmic reticulum CaATPase has a Mg(2+) ion binding sub-site.
abstract: The CaATPase of skeletal muscle sarcoplasmic reticulum was specifically labeled in the ATP binding site with fluorescein isothiocyanate under gentle conditions (pH 7 X 5). Fluorescence energy transfer from the attached fluorescein to Nd3+ indicated that a cation binding site was about 1 X 0 nm away from the fluorescein. Thus it appears that the ATP site includes a cation binding site. At 25 degrees C in 0 X 5 M KCl, the association constants for Nd3+, Ca2+ and Mg2+ were 3 X 3 X 10(5) M-1, 84 M-1 and 35 M-1, respectively, making it possible that, in vivo, the site binds Mg2+.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002413:Cations, Divalent; D016650:Fluorescein-5-isothiocyanate; D005452:Fluoresceins; D005456:Fluorescent Dyes; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism* / Q000494:pharmacology; D009132:Muscles / Q000201:enzymology*; D011485:Protein Binding; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013050:Spectrometry, Fluorescence; D013861:Thiocyanates
chemical_list: D002413:Cations, Divalent; D005452:Fluoresceins; D005456:Fluorescent Dyes; D013861:Thiocyanates; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases; D016650:Fluorescein-5-isothiocyanate; D008274:Magnesium