ISSN:
1573-4935
Keywords:
ATPase
;
calcium
;
conformational change
;
EDANS
;
fluorescence
;
sarcoplasmic reticulum
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Chemistry and Pharmacology
Notes:
Abstract Changes in the fluoresence ofN-acetyl-N′-(5-sulfo-1-naphthyl)ethylenediamine (EDANS), being attached to Cys-674 of sarcoplasmic reticulum Ca2+-ATPase without affecting the catalytic activity, as well as changes in the intrinsic tryptophan fluorescence were followed throughout the catalytic cycle by the steady-state measurements and the stopped-flow spectrofluorometry. EDANS-fluorescence changes reflect conformational changes near the ATP binding site in the cytoplasmic domain, while tryptophan-fluorescence changes most probably reflect conformational changes in or near the transmembrane domain in which the Ca2+ binding sites are located. Formation of the phosphoenzyme intermediates (EP) was also followed by the continuous flow-rapid quenching method. The kinetic analysis of EDANS-fluorescence changes andEP formation revealed that, when ATP is added to the calcium-activated enzyme, conformational changes in the ATP binding site occur in three successive reaction steps; conformational change in the calcium enzyme substrate complex, formation of ADP-sensitiveEP, and transition of ADP-sensitiveEP to ADP-insensitiveEP. In contrast, the ATP-induced tryptophan-fluorescence changes occur only in the latter two steps. Thus, we conclude that conformational changes in the ATP binding site in the cytoplasmic domain are transmitted to the Ca2+-binding sites in the transmembrane domain in these latter two steps.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01788364
