Variation of scallop sarcoplasmic reticulum Ca2+-ATPase activity with temperature

Methods for preparing native scallop sarcoplasmic reticulum vesicles, largely purified membranous scallop sarcoplasmic reticulum Ca2+-ATPase, and nonionic detergent-solubilized sarcoplasmic reticulum Ca2+-ATPase are described. The effect of a range of polyoxyethylene-based detergents on the solubilized Ca2+-ATPase was tested. Decaethylene glycol dodecyl ether (C12E10) supported the highest levels of activity, although C12E8 and C12E9 were more routinely used. Arrhenius plots of Ca2+-ATPase activity, where the assays were carried out with the same pH at all temperatures (7.4), showed a region of nonlinearity at 10 degrees C. A very similar plot was obtained when no compensation was made for pH variation with temperature. Both the break in the Arrhenius plot and the activation energies for the scallop sarcoplasmic reticulum above and below the break were very similar to those found for lobster sarcoplasmic reticulum (Madeira, V. M. C., Antunes-Madeira, M. C., and Carvalho, A. R. (1974) Biochem. Biophys. Res. Commun. 65, 997-1003). The Arrhenius plot of the scallop Ca2+-ATPase in C12E8 no longer showed the nonlinearity at 10-12 degrees C seen with the native sarcoplasmic reticulum, but instead a break now appeared at 20-21 degrees C. This is close to the Arrhenius break temperature of rabbit Ca2+-ATPase in C12E8 and of a perturbation in C12E8 (Dean, W. L. (1982) Biophys. J. 37, 56-57).