The role of histidine residues in conformational changes in the sarcoplasmic reticulum Ca-ATPase active site

Conformational pH-induced changes of Mg-ATP binding site of the sarcoplasmic reticulum Ca-ATPase (SR-ATPase) were investigated by fluorescence energy transfer between covalently bound fluorescent label (fluorescein-5-isothiocyanate, FITC) and lanthanide ion (Nd3+). These changes were approximated by...

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Bibliographic Details
Published inBiofizika Vol. 41; no. 1; p. 86
Main Authors Ivkova, M N, Vinokurov, M G, Pletnev, V V, Pechatnikov, V A
Format Journal Article
LanguageRussian
Published Russia (Federation) 01.01.1996
Subjects
Adenosine Triphosphate - metabolism
Binding Sites
Calcium-Transporting ATPases - chemistry
Calcium-Transporting ATPases - metabolism
Diethyl Pyrocarbonate - chemistry
Fluorescein-5-isothiocyanate
Fluorescent Dyes
Histidine - chemistry
Histidine - metabolism
Hydrogen-Ion Concentration
Sarcoplasmic Reticulum - enzymology
Spectrometry, Fluorescence
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Summary:Conformational pH-induced changes of Mg-ATP binding site of the sarcoplasmic reticulum Ca-ATPase (SR-ATPase) were investigated by fluorescence energy transfer between covalently bound fluorescent label (fluorescein-5-isothiocyanate, FITC) and lanthanide ion (Nd3+). These changes were approximated by simple Henderson-Hasselbach equation with the apparent pK 7.0 +/- 0.1 which is similar that of a histidyl residue [3]. In this work it was used the double chemical modification of SR-ATPase to research the role of histidyl residues in this conformational transition. Diethyl pyrocarbonate was used to modify the histidyl residues of the SR-ATPase. The influence of histidyl modification on the functional parameters (the rates of ATP and p-nitrophenyl phosphate hydrolysis, the Ca transport and the level of Ca2+ accumulation) was monitored by the fluorescent probes (Quin-2, chlortetracycline) using fluorescent, spectrophotometric and pH-metric measurements. In the result of these experiments it was found the appropriate conditions to carry out the second modification. The DEPC-SR-ATPase was labeled by FITC. The pH-dependent conformational changes in the active site of FITC-DEPC-SR-ATPase were studied by the method of the fluorescence energy transfer between FITC and Nd3+ in the region of pH 6-8. The histidyl modification of FITC-DEPC-SR-ATPase resulted in the significant shift of the curve of fluorescence energy transfer efficiency (the apparent pK > 7.5). These results suggest that the conformational transition in the active site of SR-ATPase was controlled by the histidyl residues.
ISSN:0006-3029