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Rotational Motion and Evidence for Oligomeric Structures of Sarcoplasmic Reticulum Ca2+-Activated ATPase

Winfried Hoffmann, M. Gabriela Sarzala and Dennis Chapman
Proceedings of the National Academy of Sciences of the United States of America
Vol. 76, No. 8 (Aug., 1979), pp. 3860-3864
Stable URL: http://www.jstor.org/stable/69726
Page Count: 5
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Rotational Motion and Evidence for Oligomeric Structures of Sarcoplasmic Reticulum Ca2+-Activated ATPase
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Abstract

The rotational motion of the sarcoplasmic reticulum Ca2+-activated ATPase (ATP phosphohydrolase, EC 3.6.1.3) has been investigated by measuring the decay of laser flash-induced dichroism with the covalently attached triplet probe eosin isothiocyanate. The Arrhenius plot for rotational mobility indicates two discontinuities at ≈ 15 degrees C and ≈ 35 degrees C. The experimental data are rationalized in terms of a sudden conformeric change in the ATPase at 15 degrees C and a temperature-dependent equilibrium existing between the conformationally altered ATPase and oligomeric forms of it in the temperature range 15-35 degrees C. The enzymatic activity, as indicated by a discontinuity in the Arrhenius plot for the rate of ATP hydrolysis, appears to be sensitive only to the change at 15 degrees C. There is a strong correlation between the activation energy below 15 degrees C for rotational motion (33.6 ± 2.2 kcal/mol) and enzymatic activity (34 ± 4 kcal/mol).

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