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Query: EC:3.6.3.1 (Mg2+-ATPase)
 1,484 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A technique currently used for isolation of brush border membranes from renal and intestinal epithelium that involves vigorous tissue homogenization and sedimentation of non-luminal membranes in the presence of Mg2+ has been adapted to rat liver. Liver plasma membranes so prepared consisted almost exclusively of vesicles by electron microscopy, showed some contamination with endoplasmic reticulum and minimal contamination with mitochondria or Golgi by marker enzymes, were highly enriched in alkaline phosphatase, Mg2+-ATPase, and 5'-nucleotidase activity compared with homogenate, and showed little enrichment in (Na+, K+)-ATPase. Comparison of this enzymatic profile with cytochemical studies localizing (Na+, K+)-ATPase and alkaline phosphatase to the sinusoidal/lateral and canalicular membranes, respectively, suggested that these membranes were predominantly of canalicular origin. They had a lower (Na+ + K+)-ATPase specific activity, lower lipid content, and higher cholesterol to phospholipid molar ratio than a conventional plasma membrane preparation believed to be enriched in canaliculi. Moreover, it was possible to measure movement of D-[3H]glucose into an osmotically sensitive space bounded by these membrane vesicles.
Biochim Biophys Acta 1981 Sep 07
PMID:Isolation of a rat liver plasma membrane fraction of probable canalicular origin. Preparative technique, enzymatic profile, composition, and solute transport. 611 3

Palmitoyl CoA inhibited EDTA-ATPase of heavy meromyosin (HMM) prepared from rabbit skeletal muscle. The concentration for half maximum inhibition of EDTA-ATPase was about 18 microM. Myristoyl CoA, the other long chain fatty acyl CoA, also inhibited EDTA-HMM ATPase, but CoA and short chain CoA thioesters, such as butyryl CoA, acetoacetyl CoA and acetyl CoA, at 40 microM hardly inhibited EDTA-ATPase. Less than 20% inhibition of EDTA-HMM ATPase was obtained with Na-palmitate and Na-myristate at 40 microM, whereas about 90% inhibition of the enzyme occurred in the presence of 40 microM palmitoyl CoA and myristoyl CoA. Palmitoyl carnitine, as well as carnitine, failed to inhibit EDTA-HMM-ATPase. The inhibition of palmitoyl CoA of EDTA-ATPase was reversed by bovine serum albumin and spermine. Mg2+-HMM ATPase activity was enhanced by palmitoyl CoA at 2, 5, and 10 microM. About a 25% increase in Mg2+-HMM ATPase activity was obtained at 5 and 10 microM. At higher concentrations than 20 microM, the enzyme was inhibited by palmitoyl CoA and the degree of inhibition was related to the concentration of the CoA thioester. At 80 microM, the activity was about 15% of the maximum value. The efficacy of myristoyl CoA on Mg2+-ATPase was almost the same as that of palmitoyl CoA. Mg2+-ATPase activity was not enhanced by CoA, butyryl CoA, acetoacetyl CoA, Na-myristate, Na-palmitate, palmitoyl carnitine, or carnitine at 10 microM, and was hardly reduced by these substances at 40 microM. Serum albumin and spermine also canceled, to some extent, these effects of palmitoyl CoA on Mg2+-ATPase.
J Biochem 1981 Sep
PMID:Inhibition of palmitoyl CoA of EDTA- and Mg2+-ATPase of heavy meromyosin from rabbit skeletal muscle. 611 60

Two different HMM species of gizzard myosin were prepared under conditions such that the phosphorylation of light chain was fully maintained. They were different in the N-terminal structure of the heavy chain but not in the light chain composition. A significant decrease in the Mg2+-ATPase activity was observed in one class of HMM which was proteolytically cleaved intramolecularly at site 1, 5 K daltons from the masked N terminus. Another class of HMM without the cleavage at site 1 showed ATPase activity similar to that of myosin. The decrease in ATPase activity was not caused by denaturation since similar amounts of initial burst of Pi liberation were observed with both HMMs and myosin. Kinetic and substructure analyses of HMM revealed that the activity change depended solely on the cleavage at site 1. The N-terminal region of gizzard myosin heavy chain may thus have an important role in maintaining the active site structure.
J Biochem 1981 Sep
PMID:N-terminal region of gizzard myosin heavy chain is critical for the ATPase activity. 611 61

Dopamine inhibits Mg2+,Na+,K+- and Na+,K+-ATPase activities but does not modify Mg2+-ATPase activity of nerve ending membranes isolated from rat cerebral cortex. In the presence of the soluble fraction of brain, dopamine activates total, Na+,K+-, and Mg2+-ATPases. Dopamine stimulation of nerve ending membrane ATPases is achieved when soluble fractions of brain, kidney, or liver are used. On the other hand, dopamine effects are not observed on kidney or heart ATPase preparations. The results indicate tissue specificity of dopamine effect with respect to the enzyme source; there is no tissue specificity for the requirement of the soluble fraction to achieve stimulation of ATPases by dopamine.
Neurochem Res 1981 Sep
PMID:Tissue specificity of dopamine effects on brain ATPases. 611 33

Erythrosin B (Red Dye No. 3) and Rose Bengal photosensitize the destruction of the Ca2+:Mg2+-ATPase pump protein in sarcoplasmic reticulum (SR) vesicles with respective quantum efficiencies of (1.53 +/- 0.19) X 10(-3) and (1.25 +/- 0.18) X 10(-3). Damage to vesicle function was assayed by measurements of increases in passive Ca2+ permeability. Rates of passive Ca2+ movement into the SR lumen were increased by dye photosensitization in proportion to radiation absorbed. Active Ca2+ transport into SR vesicles was blocked independent of radiation absorbed by Erythrosin B and Rose Bengal at free concentrations of 0.69 microM and 1.16 microM, respectively. The photochemical lability of the Ca2+ pump protein and alterations in passive and active Ca2+ transport may be dependent on the concentration of the dye in the membrane. The photosensitization results may have implications with respect to the suitability of Erythrosin B usage in vivo, since the brightness of our irradiation source is comparable to that of sunlight at 480 nm.
Chem Biol Interact 1982 Sep
PMID:Structural and functional degradation of Ca2+:Mg2+-ATPase rich sarcoplasmic reticulum vesicles photosensitized by erythrosin B. 612 69

The cyclic AMP-phosphodiesterase assay was used to quantitate the amount of calmodulin activity in various brain areas of male rats treated acutely or chronically for 5 days with morphine. The acute treatment with morphine decreased calmodulin activity in the mitochondrial-synaptosomal P2 fraction of the striatum, midbrain, and thalamus but had no effect on the cerebellum, which contains a low density of opiate receptors. The decrease in calmodulin activity by morphine was dose-dependent and was blocked by the opiate antagonist naloxone. In contrast, chronic treatment of rats with morphine increased calmodulin activity in the mitochondrial-synaptosomal P2 of the striatum, midbrain, cerebral cortex, and thalamus. A highly sensitive Ca2+/Mg2+-ATPase assay was also used to quantitate the amount of calmodulin activity in subcellular fractions obtained from the striatum. Chronic morphine treatment caused a significant increase in calmodulin activity in the membrane containing microsomal, synaptosomal, and mitochondrial layers but only a small change in the layer that contained the soluble proteins and the synaptic vesicles. It is suggested that alteration of the content of calmodulin in specific subcellular sites may have a central role in opiate action and addiction via regulation of multiple calmodulin-sensitive biochemical pathways.
Mol Pharmacol 1982 Sep
PMID:Effects of acute and chronic morphine treatment of calmodulin activity of rat brain. 612 69

Phosphate deficiency imposed on weanling rats for two wk resulted in a 40% increase in alkaline phosphatase activity of incisor pulp, without a significant change in Ca2+-, Mg2+-ATPase activity. The results are consistent with a separate identity for the two enzymes, but their physiological roles remain obscure.
J Dent Res 1982 Sep
PMID:Effect of phosphate deficiency on pulp alkaline phosphatase and Ca2+-, Mg2+-ATPase activity in rats. 613 38

Taxol, an antimitotic agent that induces microtubule assembly, stimulated tubulin-dependent Mg2+-ATPase activity of microtubule-associated proteins (MAPs). A concentration-dependent increase in the rate of ATP hydrolysis was observed. Taxol acted through its binding to the tubulin molecule on MAP ATPase, and maximal stimulation, which was found at approximately equal concentrations of taxol and tubulin, reached about 140% of the original level in the absence of taxol. Taxol enhanced ATP hydrolysis by a mixture of MAPs and tubulin, and this continued at a steady linear rate even when the polymerization had approached a plateau. In the presence of taxol, a large portion of ATPase activity and protein was recovered in the pellet after centrifugation at 70,000 g for 60 min at 25 degrees C. Both colchicine and podophyllotoxin inhibited taxol-stimulated ATPase activity via the same mechanism by which they inhibited taxol-induced microtubule polymerization. The stimulation by taxol was not found in the presence of Ca2+ alone but required Mg2+. We conclude that tubulin effectively stimulates Mg2+-ATPase activity of MAPs under conditions that induce tubulin polymerization.
J Neurochem 1983 Sep
PMID:Stimulation of tubulin-dependent ATPase activity in microtubule proteins from porcine brain by taxol. 613 58

In the presence of adenosine 5'-triphosphate (ATP) and 1-10 mM MgCl2, the relative viscosity (eta rel) of dephosphorylated gizzard myosin is reduced markedly over a range of KCl from 0.35 to 0.15 M. Sedimentation patterns show that the decrease in eta rel is due to the conversion of the 6S to 10S forms of myosin. Under similar conditions, eta rel of phosphorylated myosin is not altered, and at 0.2 M KCl, the 10S form is not observed. In 1 and 2 mM MgCl2 and less than 0.2 M KCl, 10S can be formed from both phosphorylated myosin plus ATP and dephosphorylated myosin minus ATP. In the presence of ethylenediaminetetraacetic acid (EDTA), the decrease of eta rel and corresponding change in sedimentation pattern are independent of ATP and show only a dependence on KCl. Therefore, ATP and dephosphorylation are not obligatory for the 6S to 10S transition. In all instances, the 6S-10S transition of monomeric myosin is paralleled by an alteration of adenosine-5'-triphosphatase (ATPase) activity; i.e., the KCl dependence of the two processes is the same. Transition from 6S to 10S causes a decrease in Mg2+-and Ca2+-ATPase activity of myosin and an increase in K+-EDTA-ATPase activity. The relationship between myosin shape and the ATP dependence of Mg2+-ATPase activity also is consistent with this generalization. The phosphorylation dependence of the viscosity transition from 6S to 10S is not linear, and phosphorylation of both heads is required for the complete transition. In contrast, the ATP dependence of the transition is linear, and the binding of 2 mol of ATP/myosin is required for maximum effect.(ABSTRACT TRUNCATED AT 250 WORDS)
Biochemistry 1983 Sep 13
PMID:Correlation of enzymatic properties and conformation of smooth muscle myosin. 613 93

Several maleimide derivatives of potential usefulness as conformational probes were tested for reactivity toward SH groups of Ca2+, Mg2+-ATPase of sarcoplasmic reticulum. These include three fluorescent labels, N-(1-anilinonaphthyl-4)maleimide (ANM), N-(p-(2-benzimidazolyl)phenyl)maleimide (BIPM), and N-(7-dimethylamino-4-methyl-3-coumarinyl)maleimide (DACM), and a spin label, 4-maleimido-2,2,6,6-tetramethylpiperidinooxyl (MSL). These reagents also exhibit a selective reactivity toward SH groups which is similar to that of N-ethylmaleimide, although these conformational probes were somewhat more reactive than N-ethylmaleimide. Based on the above finding, procedures were devised to specifically label either one of two reactive SH groups of the ATPase, namely one highly reactive but functionally nonessential (SHN) and the other, essential for the decomposition of the E-P intermediate (SHD) [Kawakita, M., et al. (1980) J. Biochem. 87, 609-617], with any one of these conformational probes. Sarcoplasmic reticulum membranes labeled with ANM at either SHN or SHD showed a characteristic fluorescence whose intensity reversibly changed in response to the removal and readdition of Ca2+ ions in the range of 10(-6) to 10(-7) M. The change could be ascribed to a conformational change of the ATPase in response to dissociation and association of Ca2+ ions at the transport site. The Ca2+-dependent fluorescence change was quantitatively different, depending on whether the ATPase was labeled at SHN or SHD. Moreover, it was probe-specific in that BIPM and DACM fluorescence did not change in response to Ca2+. The possible significance of these observations is discussed.
J Biochem 1983 Sep
PMID:Studies on conformational transitions of Ca2+, Mg2+-adenosine triphosphatase of sarcoplasmic reticulum. I. Selective labeling of functionally distinct sulfhydryl groups with conformational probes and evidence for a Ca2+-dependent conformational change. 613 70


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