Premium
Strontium binding to sarcoplasmic reticulum Ca 2+ ‐ATPase
Author(s) -
Orlowski Stéphane,
Champeil Philippe
Publication year - 1993
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(93)80947-s
Subject(s) - chemistry , fluorescence , atpase , endoplasmic reticulum , vesicle , calcium atpase , fluorescein isothiocyanate , biophysics , binding site , ion transporter , atp hydrolysis , biochemistry , membrane , enzyme , biology , physics , quantum mechanics
We investigated the consequences of Sr 2+ binding to the transport sites of sarcoplasmic reticulum (SR) Ca 2+ ‐ATPase for two fluorescent conformational probes located in different regions of the ATPase. Using SR vesicles in which Lys‐515 in the ATPase had been previously labeled with fluorescein 5'‐isothiocyanate (FITC), we found that the Sr 2+ ‐induced a drop in the fluorescein fluorescence of this FITC‐labeled ATPase shifted toward lower Sr 2+ concentrations than the Sr 2+ ‐induced rise in Trp fluorescence for the same FITC‐labeled ATPase. The curve describing the Sr 2+ ‐dependent rise in Trp fluorescence had a characteristic asymmetric shape, and the changes in Trp fluorescence occurred in parallel with the activation by Sr 2+ of pNPP hydrolysis by the ATPase. Analysis of these results in terms of the simplest scheme describing the sequential binding of the two Sr 2+ ions suggests that under the conditions of these experiments, i.e. at neutral pH in the presence of potassium, the Sr 2+ ‐induced rise in the Trp fluorescence mainly reflected the formation of ATPase with two ions bound to the transport sites, whereas the binding of a single Sr 2+ ion was virtually sufficient to reduce the fluorescence of bound FITC to its minimal level.