scholarly journals Interference of Nucleoside Diphosphates and Inorganic Phosphate with Nucleoside-Triphosphate-Dependent Calcium Fluxes and Calcium-Dependent Nucleoside-Triphosphate Hydrolysis in Membranes of Sarcoplasmic-Reticulum Vesicles

1981 ◽  
Vol 116 (3) ◽  
pp. 601-608 ◽  
Author(s):  
Wolfgang WAAS ◽  
Wilhelm HASSELBACH
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Inorganic Phosphate ◽  
Nucleoside Triphosphate ◽  
Calcium Fluxes ◽  
Calcium Dependent

Pressure Effects on the Interactions of the Sarcoplasmic Reticulum Calcium Transport Enzyme with Calcium and para-Nitrophenyl Phosphate

1987 ◽  
Vol 42 (5) ◽  
pp. 641-652 ◽  
Author(s):  
Wilhelm Hasselbach ◽  
Lore Stephan
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Transport ◽  
Activation Volume ◽  
Reaction Scheme ◽  
Pressure Effects ◽  
Calcium Dependent ◽  
Nitrophenyl Phosphate ◽  
Hydrolysis Of ◽  
Sarcoplasmic Reticulum Calcium ◽  
Effect Of Hydrostatic Pressure

The effect of hydrostatic pressure on calcium dependent p-nitrophenyl phosphate hydrolysis of the sarcoplasmic reticulum calcium transport enzyme has been investigated at different degree of enzyme saturation by calcium and Mg-p-nitrophenyl phosphate to distinguish between activation and binding volumes. The enzyme saturated by both ligands displays a significant dependence of the activation volume on pressure, rising from 20 ml/mol at atmospheric pressure (0.1 MPa) to 80 ml/mol at 100 MPa. At subsaturating concentration of Mg-p-nitrophenyl phosphate an activation volume of 35 ml/mol prevails between 0.1 and 40 MPa. At subsaturating concentration of calcium the activation volume approximates 80 ml/mol in the same pressure range. The binding volume for both substrates is likewise pressure dependent falling from 20 ml/mol to 0 ml/mol for Mg-p-nitrophenyl phosphate and rising from 67 ml/mol to 155 ml/mol for calcium. The pressure dependence of activation and binding volumes is analysed on account of a simplified reaction scheme yielding activation volumes and rate constants for individual reaction steps.

The Effect of Calcium and Phosphate on the Biphasic Calcium Uptake by the Sarcoplasmic Reticulum

1975 ◽  
Vol 30 (11-12) ◽  
pp. 777-780 ◽  
Author(s):  
Pierre Ermier ◽  
Wilhelm Hasselbach
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Inorganic Phosphate ◽  
Calcium Uptake ◽  
Initial Rate ◽  
Maximum Amplitude ◽  
Phosphate Concentration ◽  
Free Calcium ◽  
Physiological Range ◽  
External Calcium

Abstract The amplitude of the fast uptake and the initial rate of the slow uptake increase with in­ creasing free calcium concentrations, up to 30 μᴍ. In that range, both processes are correlated to each other. At higher concentrations, the slow uptake is more inhibited than the fast uptake. The fast uptake shows a maximum amplitude which remains unchanged in the presence of phosphate. The slow uptake leads to a nearly complete depletion of the external calcium, and its rate is proportional to the phosphate concentration, even at physiological range. The sarcoplasmic ATPase liberates inorganic phosphate and the slow uptake

Effect of Non-Solubilizing SDS Concentrations on High Affinity Ca2+ Binding and Steady State Phosphorylation by Inorganic Phosphate of the Sarcoplasmic Reticulum ATPase

1989 ◽  
Vol 44 (1-2) ◽  
pp. 139-152 ◽  
Author(s):  
Elisabeth Fassold ◽  
Wilhelm Hasselbach ◽  
Bernd Küchler
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Inorganic Phosphate ◽  
Atp Hydrolysis ◽  
Mutual Exclusion ◽  
Chemical Properties ◽  
Cooperative Interaction ◽  
Hydrophobic Force ◽  
High Affinity ◽  
Binding Domains ◽  
Phosphorylation Domain

Abstract In this investigation low, non-solubilizing concentrations of the strong anionic detergent SDS were used to perturbate the interaction of Ca2+ and Pi with their respective binding domains on the sarcoplasmic reticulum Ca-transport ATPase. Rising SDS concentrations produce a two-step decline of Ca2+-dependent ATP hydrolysis. At pH 6.15, SDS differently affects high affinity Ca2+ binding and phosphorylation by inorganic phosphate and releases the “mutual exclusion” of these two ligand binding steps. The degree of uncoupling is considerably more pronounced in the presence of 20% Me2SO. The reduction of Ca2+ binding by SDS is demonstrated to be a result of decreased affinity of one of the two specific high affinity binding sites and of perturbation of their cooperative interaction. Higher SDS partially restores the original high Ca2+ affinity but not the cooperativity of binding. Phosphorylation exhibits a higher SDS sensitivity than Ca2+ binding: Increasing SDS competitively inhibits and then completely abolishes phosphoenzyme formation. Thus. SDS binds to the phosphorylation domain, evidently involving the Lys352 residue of the ATPase molecule; this is accompanied by a more unspecific concentration-dependent SDS effect, probably mediated by hydrophobic force, which, finally, suppresses phosphorylation. Me2SO does neither qualitatively affect the SDS-dependent chemical properties of the vesicular material nor the SDS-dependent perturbation of the investigated reaction steps.

scholarly journals The Effect of Calcium Ionophores on Fragmented Sarcoplasmic Reticulum

1972 ◽  
Vol 60 (6) ◽  
pp. 735-749 ◽  
Author(s):  
Antonio Scarpa ◽  
Judith Baldassare ◽  
Giuseppe Inesi
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Binding ◽  
Calcium Release ◽  
Atp Hydrolysis ◽  
Divalent Cations ◽  
Electron Microscopic ◽  
Microscopic Appearance ◽  
Calcium Accumulation ◽  
Calcium Dependent ◽  
Dependent Atpase

X-537 A and A 23187, two antibiotics which form liphophilic complexes with divalent cations, function as ionophores in vesicular fragments of sarcoplasmic reticulum (SR). Addition of either ionophore to SR preloaded with calcium in the presence of adenosine triphosphate (ATP), causes rapid release of calcium. Furthermore, net calcium accumulation by SR is prevented, when the ionophores are added to the reaction mixture before ATP. On the contrary, ATP-independent calcium binding to SR is not inhibited. This effect is specific for the two antibiotics and could not be reproduced, either by inactive derivatives, or by other known ionophores. Neither ionophore produces alterations of the electron microscopic appearance of SR membranes or inhibition of the calcium-dependent ATPase. In fact, the burst of ATP hydrolysis obtained on addition of calcium, is prolonged in the presence of the ionophores. Lanthanum inhibits ATP-independent calcium binding to SR, ATP-dependent calcium accumulation and calcium-dependent ATPase. However, addition of lanthanum to SR preloaded in the presence of ATP, does not cause calcium release. The reported experiments indicated that: (a) ATP-dependent calcium accumulation by SR results in primary formation of calcium ion gradients across the membrane. (b) Most of the accumulated calcium is not available for displacement by lanthanum on the outer surface of the membrane. (c) Calcium ionophores induce rapid equilibration of the gradients, by facilitating cation diffusion across the membrane.

Calcium-dependent halothane activation of sarcoplasmic reticulum calcium channels from frog skeletal muscle

1994 ◽  
Vol 266 (2) ◽  
pp. C391-C396 ◽  
Author(s):  
R. Bull ◽  
J. J. Marengo
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Calcium Channels ◽  
Lipid Bilayers ◽  
Single Channel ◽  
Free Calcium ◽  
Frog Skeletal Muscle ◽  
Time Constants ◽  
Calcium Dependent ◽  
Open Time

The effect of halothane on calcium channels present in sarcoplasmic reticulum membranes isolated from frog skeletal muscle was studied at the single channel level after fusing the isolated vesicles into planar lipid bilayers. Addition of 91 microM halothane to the cytosolic compartment containing 1 microM free calcium activated the channel by increasing fractional open time from 0.11 to 0.59, without changing the channel conductance. The activation of the channels by halothane was calcium dependent. At resting calcium concentrations in the cytosolic compartment, halothane failed to activate the channel, whereas maximal activation was found at 10 microM calcium. The free energy of halothane binding to the channel decreased from -5.8 kcal/mol at 1 microM calcium to -6.6 kcal/mol at 10 microM calcium. Halothane increased the open time constants and decreased the closed time constants, indicating that it binds to both the open and the closed configurations of the channel.

Low concentrations of A23187 increase calcium uptake by cardiac sarcoplasmic reticulum

1985 ◽  
Vol 249 (6) ◽  
pp. H1211-H1215
Author(s):  
J. J. Murray ◽  
A. V. Kuzmin ◽  
P. W. Reed ◽  
D. O. Levitsky
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Calcium Uptake ◽  
Atp Hydrolysis ◽  
Ionophore A23187 ◽  
Uptake System ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Cardiac Sarcoplasmic Reticulum ◽  
Calcium Dependent ◽  
Uptake Measurement

The divalent cation ionophore A23187 at a concentration of 1 nM produced an increased rate of oxalate-supported calcium uptake by isolated cardiac sarcoplasmic reticulum as determined by absorbance changes of the calcium-sensitive dye murexide. Addition of a higher concentration of A23187 (0.1 microM) produced a decreased rate of calcium uptake. Measurement of the time during which ATPase was activated by calcium addition also suggested an increased rate of calcium uptake in the presence of 1 nM A23187 and an inhibition of calcium uptake at a higher concentration of the ionophore (0.1 microM). Ca2+-stimulated ATPase activity and incorporation of 32Pi from [gamma-32P]ATP into sarcoplasmic reticular proteins were increased by A23187 at concentrations of 1 nM or greater. An increased coupling of calcium uptake to ATP hydrolysis was observed at 1 nM A23187, while concentrations of the ionophore greater than or equal to 10 nM produced a decreased coupling. Addition of an inhibitor of cyclic AMP-dependent protein kinase decreased the rate of calcium uptake, and this inhibition was reversed in a concentration-dependent manner by 0.01–1 nM A23187. These data suggest that A23187 can activate a mechanism involving the calcium-dependent phosphorylation of protein that may regulate the activity of the calcium uptake system of the sarcoplasmic reticulum. These observations appear to provide an explanation for some of the contractile effects of A23187 in intact cardiac muscle that suggest that treatment with the ionophore results in an increased sequestration of calcium from the cytoplasm.

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