Rotational motion and evidence for oligomeric structures of sarcoplasmic reticulum Ca2+-activated ATPase.
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 approximately 15 degrees C and approximately 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).
D000818:Animals; D000252:Calcium-Transporting ATPases; D004058:Diffusion; D004789:Enzyme Activation; D046911:Macromolecular Substances; D009038:Motion; D011487:Protein Conformation; D011817:Rabbits; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*; D013696:Temperature; D013816:Thermodynamics
D046911:Macromolecular Substances; D000252:Calcium-Transporting ATPases