scholarly journals A model for the phosphorylation of the Ca2+ + Mg2+-activated ATPase by phosphate

1986 ◽  
Vol 237 (1) ◽  
pp. 207-215 ◽  
Author(s):  
R J Froud ◽  
A G Lee
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Fluorescence Intensity ◽  
Fluorescein Isothiocyanate ◽  
Fluorescence Response

We have shown that changes in fluorescence intensity for the Ca2+ + Mg2+-activated ATPase of sarcoplasmic reticulum labelled with fluorescein isothiocyanate following the addition of Ca2+ can give the ratio of the two conformations (E1 and E2) of the ATPase. We show that the fluorescence response to Ca2+ is unaffected by Mg2+, phosphate or K+, implying that these ions bind equally well to the E1 and E2 conformations. A model is presented for phosphorylation of the ATPase by phosphate as a function of pH, Mg2+, K+ and Ca2+.

scholarly journals The effects of membrane potential and lanthanides on the conformation of the Ca2+-transport ATPase in sarcoplasmic reticulum

1986 ◽  
Vol 234 (2) ◽  
pp. 363-371 ◽  
Author(s):  
I Jona ◽  
A Martonosi
Keyword(s):  
Membrane Potential ◽  
Sarcoplasmic Reticulum ◽  
Fluorescence Intensity ◽  
Binding Sites ◽  
Fluorescein Isothiocyanate ◽  
Tryptophan Fluorescence ◽  
Lanthanide Ions ◽  
Positive Potential ◽  
High Affinity ◽  
Ion Substitution

The effects of Ca2+, lanthanide ions (Gd3+, La3+ and Pr3+) and membrane potential on the fluorescence of tryptophan and covalently bound fluorescein were analysed in native and fluorescein isothiocyanate (FITC)-labelled sarcoplasmic reticulum vesicles. The binding of Ca2+ and lanthanides to the Ca2+-ATPase increases the fluorescence intensity of tryptophan and decreases the fluorescence intensity of FITC; the dependence of these effects on cation concentration is consistent with the involvement of the high-affinity Ca2+-binding sites of the Ca2+-ATPase in the cation-induced fluorescence changes. The fluorescence of FITC-labelled sarcoplasmic reticulum vesicles is also influenced by membrane potential changes induced by ion substitution. Inside positive potential increases, while inside negative potential decreases, the fluorescence of bound FITC. Smaller potential-dependent changes in tryptophan fluorescence were also observed. The effects of Ca2+, lanthanides and membrane potential on the fluorescence of tryptophan and FITC are discussed in terms of the two major conformations of the Ca2+-ATPase (E1 and E2), that are assumed to alternate during Ca2+ transport. The observations support the suggestion [Dux, Taylor, Ting-Beall & Martonosi (1985) J. Biol. Chem. 260, 11730-11743] that the vanadate-induced crystals of Ca2+-ATPase represent the E2, while the Ca2+ and lanthanide-induced crystals the E1, conformation of the enzyme.

Effects of polymyxin B on the sarcoplasmic reticulum membrane

1989 ◽  
Vol 9 (5) ◽  
pp. 573-578 ◽  
Author(s):  
T. B. Ktenas ◽  
T. G. Sotiroudis ◽  
A. E. Evangelopoulos
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Fluorescence Intensity ◽  
Cyclic Peptide ◽  
Fluorescein Isothiocyanate ◽  
Polymyxin B ◽  
The Other ◽  
Peptide Antibiotic ◽  
Phosphorylase Kinase ◽  
Sarcoplasmic Reticulum Membrane

Polymyxin B, a cyclic peptide antibiotic, inhibits Ca2+-ATPase, p-nitrophenyl phosphatase and phosphorylase kinase activities associated with rabbit skeletal muscle sarcoplasmic reticulum membranes; 50% inhibition is induced by 100 μM, 130μM and 550 μM of polymyxin respectively. The fluorescence intensity of fluorescein isothiocyanate-labeled Ca2+-ATPase, decreases in the presence of polymyxin (50% of the total decrease at 70 μM polymyxin). On the other hand, the polypeptide inhibits calmodulin-dependent endogenous phosphorylation of 60 kDa, 20 kDa and 14 kDa membrane proteins, while an increase of calmodulin-dependent phosphorylation is observed in 132 kDa and 86 kDa proteins.

Intracellular Ca2+ levels and amylase secretion in Quin 2-loaded mouse pancreatic acini

1985 ◽  
Vol 248 (5) ◽  
pp. C535-C541 ◽  
Author(s):  
R. E. Powers ◽  
P. C. Johnson ◽  
M. J. Houlihan ◽  
A. K. Saluja ◽  
M. L. Steer
Keyword(s):  
Fluorescence Intensity ◽  
Fluorescence Probe ◽  
Amylase Secretion ◽  
Extracellular Medium ◽  
Pancreatic Acini ◽  
Cholecystokinin Octapeptide ◽  
Fluorescence Response ◽  
Cholinergic Antagonist ◽  
Initial Rise ◽  
Plateau Level

Dispersed mouse pancreatic acini were loaded with the Ca2+-sensitive fluorescence probe Quin 2. Stimulation with carbamylcholine or cholecystokinin-octapeptide (CCK-OP) resulted in a rapid increase in Quin 2 fluorescence, which returned to a lower and sustained plateau level within 2 min of secretagogue stimulation. The magnitude of the initial rise in fluorescence intensity and of amylase secretion were closely related to the concentration of agonist used. Maximal fluorescence changes and amylase secretion were noted with 1 X 10(-5) M carbamylcholine and 1 X 10(-9) M CCK-OP, whereas both responses were half maximal in the presence of 5 X 10(-7) M carbamylcholine and approximately 1 X 10(-10) M CCK-OP. The resting cytosolic free Ca2+ concentration, as measured by the intensity of Quin 2 fluorescence, was calculated to be 1.03 +/- 0.12 X 10(-7) M. Cytosolic free Ca2+ rose to 1.3 +/- 0.3 X 10(-6) M after addition of 1 X 10(-5) M carbamylcholine and 1.25 +/- 0.21 X 10(-6) M following 1 X 10(-9) M CCK-OP. Amylase secretion, but not the Quin 2 fluorescence response, was attenuated at higher secretagogue concentrations. Both secretagogue-induced Quin 2 fluorescence and amylase secretion were inhibited by secretagogue antagonists. Removal of Ca2+ from the extracellular medium resulted in a 48.8 +/- 2.0% reduction of carbamylcholine-induced Quin 2 fluorescence. Following addition of carbamylcholine, CCK-OP was unable to stimulate a second increase in Quin 2 fluorescence without the intervening addition of a cholinergic antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Inactivation of sarcoplasmic-reticulum Ca2+-ATPase in low-frequency-stimulated muscle results from a modification of the active site

1992 ◽  
Vol 285 (1) ◽  
pp. 303-309 ◽  
Author(s):  
S Matsushita ◽  
D Pette
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Active Site ◽  
Low Frequency ◽  
Fluorescein Isothiocyanate ◽  
Tryptophan Fluorescence ◽  
Atp Binding ◽  
Binding Characteristics ◽  
Intrinsic Tryptophan Fluorescence ◽  
Inactive Form ◽  
Induced Changes

Molecular changes underlying the partial inactivation of the sarcoplasmic-reticulum (SR) Ca(2+-) ATPase in low-frequency-stimulated fast-twitch muscle were investigated in the present study. The specific Ca(2+)-ATPase activity, as well as the ATP- and acetyl phosphate-driven Ca2+ uptakes by the SR, were reduced by approx. 30% in 4-day-stimulated muscle. Phosphoprotein formation of the enzyme in the presence of ATP or Pi was also decreased to the same extent. Measurements of ATP binding revealed a 30% decrease in binding to the enzyme. These changes were accompanied by similar decreases in the ligand-induced (ATP, ADP, Pi) intrinsic tryptophan fluorescence. A decreased binding of fluorescein isothiocyanate (FITC) corresponded to the lower ATP binding and phosphorylation of the enzyme. Moreover, Pi-induced changes in fluorescence of the FITC-labelled enzyme did not differ between SR from stimulated and contralateral muscles, indicating that Ca(2+)- ATPase molecules which did not bind FITC were responsible for the decreased Pi-dependent phosphorylation, and therefore represented the inactive form of the enzyme. No differences existed between the Ca(2+)-induced changes in the intrinsic fluorescence of SR from stimulated and contralateral muscles which fit their similar Ca(2+)-binding characteristics. Taking the proposed architecture of the Ca2(+)-ATPase into consideration, our results suggest that the inactivation relates to a circumscribed structural alteration of the enzyme in sections of the active site consisting of the nucleotide-binding and phosphorylation domains.

Sign in / Sign up

Export Citation Format

Share Document