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Evaluation of H2O activity in the free or phosphorylated catalytic site of Ca2+-ATPase |
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| Authors: | Y Dupont R Pougeois |
| Affiliation: | 1. Laboratoire de Biologie Moléculaire et Cellulaire, ER 199 CNRS, Département de Recherches Fondamentales, Centre d''Etudes Nucléaires de Grenoble, BP 85X, 38041 Grenoble, France;2. Laboratoire de Biochimie Endocrinienne, INSERM 244, ERA 942 CNRS, CERMO, Université de Grenoble, BP 68, 38402 Saint Martind''Heres, France |
| Abstract: | The sarcoplasmic reticulum Ca2+-ATPase catalyses a reversible calcium transport coupled to phosphate transfer between ATP and water. It has been proposed [Biochemistry (1980) 19, 4252-4261] that the reactivity of the acyl-phosphate bond is dependent on the water activity within the catalytic site. We have tested this hypothesis and found that the polarity in the free catalytic site is lower than that of water, a further and large decrease is observed when the enzyme is phosphorylated by Pi. Phosphorylation by ATP indicates that this polarity change is specifically associated with the formation of the ADP-insensitive phosphoenzyme. |
| Keywords: | Sarcoplasmic reticulum Energy transduction Phosphorylation Water Fluorescence Tris tris(hydroxymethyl)-aminomethane MES morpholinoethane-sulphonic acid EGTA TNP–ATP |
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