Evidence that the ATP binding site of sarcoplasmic reticulum CaATPase has a Mg(2+) ion binding sub-site |
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Authors: | S Highsmith |
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Institution: | Department of Biochemistry School of Dentistry University of the Pacific San Francisco, CA 94115 USA |
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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+. |
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