Effect of calcium concentration on isolated hamster brain Na-K-, Mg-dependent ATPase

1982 ◽  
Vol 60 (8) ◽  
pp. 1119-1124 ◽  
Author(s):  
F. Rohani ◽  
J. D. Welty ◽  
D. F. Hastings
Keyword(s):  
Atpase Activity ◽  
Binding Site ◽  
Calcium Binding ◽  
Calcium Concentration ◽  
Specific Activity ◽  
Hill Coefficient ◽  
Affinity Binding ◽  
Dependent Atpase ◽  
Positive Cooperativity

In these experiments the effect of different concentrations of calcium on the specific activity of isolated Na-K-ATPase was studied. The result of these investigations showed that calcium at 10−6 and 10−7 M stimulated the Na-K-ATPase activity. These studies also show that at higher calcium concentrations (10−5–10−3 M), the activity of the enzyme is inhibited. The results from calcium binding to isolated membranes, rich in Na-K-ATPasc, strongly suggest the existence of a low-affinity binding site which exhibits a large positive cooperativity, Kd = 2.8 × 10−5 ± 0.4 × 10−5 M and Hill coefficient of 2.9 ± 0.2. The calcium concentration (1.9 × 10−5 M sufficient to produce significant (24%) inhibition of the Na-K-ATPase is approximately equal to the Kd observed for calcium binding.

scholarly journals Characterization of Ca2+ interactions with matrix metallopeptidase-12: implications for matrix metallopeptidase regulation

2006 ◽  
Vol 398 (3) ◽  
pp. 393-398 ◽  
Author(s):  
Thomas Gossas ◽  
U. Helena Danielson
Keyword(s):  
Binding Site ◽  
Binding Sites ◽  
Calcium Binding ◽  
Three Dimensional ◽  
Zinc Ion ◽  
Affinity Binding ◽  
High Affinity Binding ◽  
High Affinity ◽  
High Affinity Binding Site ◽  
Matrix Metallopeptidase

Matrix metallopeptidase-12 (MMP-12) binds three calcium ions and a zinc ion, in addition to the catalytic zinc ion. These ions are thought to have a structural role, stabilizing the active conformation of the enzyme. To characterize the importance of Ca2+ binding for MMP-12 activity and the properties of the different Ca2+ sites, the activity as a function of [Ca2+] and the effect of pH was investigated. The enzymatic activity was directly correlated to calcium binding and a Langmuir isotherm for three binding sites described the activity as a function of [Ca2+]. The affinities for two of the binding sites were quantified at several pH values. At pH 7.5, the KD was 0.1 mM for the high-affinity binding site, 5 mM for the intermediate-affinity binding site and >100 mM for the low-affinity binding site. For all three sites, the affinity for calcium decreased with reduced pH, in accordance with the loss of interactions upon protonation of the calcium-co-ordinating aspartate and glutamate carboxylates at acidic pH. The pKa values of the calcium binding sites with the highest and intermediate affinities were determined to be 4.3 and 6.5 respectively. Optimal pH for catalysis was above 7.5. The low-, intermediate- and high-affinity binding sites were assigned on the basis of analysis of three-dimensional-structures of MMP-12. The strong correlation between MMP-12 activity and calcium binding for the physiologically relevant [Ca2+] and pH ranges studied suggest that Ca2+ may be involved in controlling the activity of MMP-12.

Contractile proteins and sarcoplasmic reticulum in physiologic cardiac hypertrophy

1981 ◽  
Vol 241 (2) ◽  
pp. H263-H267 ◽  
Author(s):  
A. Malhotra ◽  
S. Penpargkul ◽  
T. Schaible ◽  
J. Scheuer
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Calcium Binding ◽  
Wistar Rats ◽  
Calcium Concentration ◽  
Calcium Uptake ◽  
Contractile Proteins ◽  
Heart Weight ◽  
Female Wistar Rats ◽  
Female Control

To study effects of physiologic hypertrophy on contractile protein ATPases and sarcoplasmic reticulum, hypertrophy was caused in female Wistar rats by a chronic swimming program. Nonhypertrophied hearts of female control sedentary rats and rats made to run on a treadmill program were also examined. The swimming program, but not the running program, resulted in a significant increase in heart weight. Actomyosin ATPase activity was also increased by 15% in the hearts of swimmers but not runners. Similar increases were observed for Ca2+-activated myosin ATPase activity and actin-activated ATPase of myosin. Sarcoplasmic reticulum from the hearts of swimmers showed increased calcium binding and calcium uptake as a function of time and of calcium concentration. Sarcoplasmic reticulum ATPase activities were not altered by hypertrophy. These findings in physiologic hypertrophy contrast with those of pathologic hypertrophy in which ATPase activity of contractile proteins and calcium binding and uptake of sarcoplasmic reticulum have generally been found to be depressed.

Effects of lanthanum on the heart sarcolemmal ATPase and calcium binding activities

1979 ◽  
Vol 57 (5) ◽  
pp. 496-503 ◽  
Author(s):  
Satoshi Takeo ◽  
Peter Duke ◽  
Gina M. L. Taam ◽  
Pawan K. Singal ◽  
Naranjan S. Dhalla
Keyword(s):  
Atpase Activity ◽  
Calcium Binding ◽  
Calcium Concentration ◽  
Treatment Method ◽  
Binding Activity ◽  
Outer Cell ◽  
Control Value ◽  
Rat Hearts ◽  
Dense Deposits ◽  
Perfused Hearts

Effects of lanthanum on Ca2+-ATPase, Mg2+-ATPase, Na+–K+-ATPase, and calcium binding activities were studied in rat heart sarcolemma. Ten to 100 μM lanthanum depressed significantly the Ca2+-ATPase activity and 50–200 μM lanthanum inhibited the calcium binding activity. Lineweaver–Burk plots of the Ca2+-ATPase activity showed that the inhibition by lanthanum was competitive with calcium concentration. Neither Mg2+-ATPase nor Na+–K+-ATPase activities were affected by lanthanum when the assay medium contained 1 mM EDTA; however, in the absence of EDTA, these enzyme activities were significantly decreased by 10–100 μM lanthanum. Rat hearts perfused with HEPES buffer containing 0.5 mM lanthanum showed electron-dense deposits restricted to the outer cell surface and the sarcolemma obtained from these hearts also had the deposits, indicating that the membrane fraction isolated by the hypotonic shock – LiBr treatment method is of sarcolemmal origin. The Ca2+-ATPase activity of the sarcolemma isolated from lanthanum-perfused hearts, unlike the Mg2+-ATPase, Na+–K+-ATPase, and calcium binding activities, was significantly less than the control value. From these observations it is suggested that lanthanum may influence calcium movement across the sarcolemma by affecting sarcolemmal ATPase and calcium binding activities.

Human muscle sarcoplasmic reticulum function during submaximal exercise in normoxia and hypoxia

2004 ◽  
Vol 97 (1) ◽  
pp. 180-187 ◽  
Author(s):  
T. A. Duhamel ◽  
H. J. Green ◽  
J. G. Perco ◽  
S. D. Sandiford ◽  
J. Ouyang
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Atpase Activity ◽  
Vastus Lateralis ◽  
Maximal Activity ◽  
Human Muscle ◽  
Hill Coefficient ◽  
Moderate Intensity ◽  
Vastus Lateralis Muscle ◽  
Moderate Intensity Exercise ◽  
Dependent Atpase

In this study, the response of the sarcoplasmic reticulum (SR) to prolonged exercise, performed in normoxia (inspired O2 fraction = 0.21) and hypoxia (inspired O2 fraction = 0.14) was studied in homogenates prepared from the vastus lateralis muscle in 10 untrained men (peak O2 consumption = 3.09 ± 0.25 l/min). In normoxia, performed at 48 ± 2.2% peak O2 consumption, maximal Ca2+-dependent ATPase activity was reduced by ∼25% at 30 min of exercise compared with rest (168 ± 10 vs. 126 ± 8 μmol·g protein−1·min−1), with no further reductions observed at 90 min (129 ± 6 μmol·g protein−1·min−1). No changes were observed in the Hill coefficient or in the Ca2+ concentration at half-maximal activity. The reduction in maximal Ca2+-dependent ATPase activity at 30 min of exercise was accompanied by oxalate-dependent reductions ( P < 0.05) in Ca2+ uptake by ∼20% (370 ± 22 vs. 298 ± 25 μmol·g protein−1·min−1). Ca2+ release, induced by 4-chloro- m-cresol and assessed into fast and slow phases, was decreased ( P < 0.05) by ∼16 and ∼32%, respectively, by 90 min of exercise. No differences were found between normoxia and hypoxia for any of the SR properties examined. It is concluded that the disturbances induced in SR Ca2+ cycling with prolonged moderate-intensity exercise in human muscle during normoxia are not modified when the exercise is performed in hypoxia.

scholarly journals The differential release of basal ATPase, Ca2+-dependent ATPase, 5′-nucleotidase and cholesterol during homogenization of skeletal muscle

1980 ◽  
Vol 188 (2) ◽  
pp. 569-572 ◽  
Author(s):  
E J Barrett ◽  
N M Ryan ◽  
D R Headon
Keyword(s):  
Skeletal Muscle ◽  
Atpase Activity ◽  
Microsomal Fraction ◽  
Specific Activity ◽  
Fragmentation Pattern ◽  
Specific Concentration ◽  
Dependent Atpase

The influence of homogenization times on the presence of constituents in the microsomal fraction of skeletal muscle was investigated. Membranes having Ca2+-activated ATPase activity have a fragmentation pattern distinct from that of membranes displaying Ca2+-independent or basal ATPase activity. These latter membranes were found in highest specific concentration in the microsomal fraction prepared from homogenates subjected to short periods of homogenization. 5′-Nucleotidase (EC 3.1.3.5) activity paralleled that of basal ATPase on short periods of homogenization, as also did the specific concentration of cholesterol. Longer periods of homogenization led to a decrease in the specific activity of basal atpase, which reached its lowest value at 120s of homogenization, whereas the specific activity of 5′-nucleotidase and the specific concentration of cholesterol decreased initially in a similar manner to basal ATPase, but both increased substantially after the longest period of homogenization.

scholarly journals Hepatic endosome fractions contain an ATP-driven proton pump

1985 ◽  
Vol 225 (1) ◽  
pp. 51-58 ◽  
Author(s):  
T Saermark ◽  
N Flint ◽  
W H Evans
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Apparatus ◽  
Atpase Activity ◽  
Proton Pump ◽  
Subcellular Distribution ◽  
Plasma Membranes ◽  
Specific Activity ◽  
Ph Gradients ◽  
Subcellular Organelle ◽  
Liver Homogenates

Endosome fractions were isolated from rat liver homogenates on the basis of the subcellular distribution of circulating ligands, e.g. 125I-asialotransferrin internalized by hepatocytes by a receptor-mediated process. The distribution of endocytosed 125I-asialotransferrin 1-2 min and 15 min after uptake by liver and a monensin-activated Mg2+-dependent ATPase activity coincided on linear gradients of sucrose and Nycodenz. The monensin-activated Mg2+-ATPase was enriched relative to the liver homogenates up to 60-fold in specific activity in the endosome fractions. Contamination of the endosome fractions by lysosomes, endoplasmic reticulum, mitochondria, plasma membranes and Golgi-apparatus components was low. By use of 9-aminoacridine, a probe for pH gradients, the endosome vesicles were shown to acidify on addition of ATP. Acidification was reversed by addition of monensin. The results indicate that endosome fractions contain an ATP-driven proton pump. The ionophore-activated Mg2+-ATPase in combination with the presence of undegraded ligands in the endosome fractions emerge as linked markers for this new subcellular organelle.

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