Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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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)

The effect of cholesterol and fatty acid treatment in vitro was tested on rat liver plasma membrane-bound enzymes and lipid fluidity. The observed alterations of membrane fluidity affect both (Na+-K+)-ATPase and Mg2+-ATPase activities but not 5'-nucleotidase; basal adenylate cyclase as well as its hormonal sensitivity were differentially affected by changes of membrane microenvironment.
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PMID:Effect of free fatty acids and cholesterol in vitro on liver plasma membrane-bound enzymes. 612 91

1. The plasma membrane of the flounder erythrocyte contains a Mg2+-dependent ATPase which is insensitive to ouabain. Mg2+ is part of the substrate, Mg-ATP, and Mg2+ also functions as a nonessential activator. 2. Ca2+, Mn2+ and Co2+ can replace Mg2+ as an activator of ATP hydrolysis. Cu2+ and Zn2+ abolish the Mg-dependent activity. It is shown that Ca2+ and Mg2+ activate the same enzyme and that Mg-ATP and Ca-ATP are mutually competitive. 3. The hydrolysis of ATP obeys Michaelis-Menten kinetics whether or not the Mg2+-ATPase is fully activated by Mg2+. The KM values for Mg-ATP were found to be 0.13 and 0.43 mM respectively. 4. Free ATP acts as a competitive inhibitor towards Mg-ATP and the dissociation constant for the enzyme-ATP complex was determined to be about 0.55 mM. 5. The Mg2+ -ATPase has a low specificity and reacts with the common nucleoside triphosphates GTP, ITP, UTP and CTP. 6. The enzyme has a broad pH optimum ranging from 6.5 to 7.2 and an energy of activation of 13.5 kcal/mol between 0 and 30 degrees C. 7. The effect of some activators and inhibitors of membrane-bound ATPases are reported.
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PMID:The Mg2+-dependent ATPase from the erythrocyte plasma membrane of the flounder Platichthys flesus L. General properties and some observations on the steady state kinetics. 613 79

Highly purified plasma membranes of calf thymocytes were fractionated by means of affinity chromatography on concanavalin A-Sepharose into two subfractions; one (fraction 1) eluted freely from the affinity column, the second (fraction 2) adhered specifically to concanavalin A-Sepharose. Previous analysis showed that both subfractions were right-side-out (Resch, K., Schneider, S. and Szamel, M. (1981) Anal. Biochem. 117, 282-292). The ratio of cholesterol to phospholipid was nearly identical in plasma membrane and both subfractions. When isolated plasma membranes were labelled with tritiated NaBH4, both subfractions exhibited identical specific radioactivities. After enzymatic radioiodination of thymocytes, the relative distribution of labelled proteins and externally exposed phospholipids was very similar in isolated plasma membranes and in both membrane subfractions, indicating the plasma membrane nature of the subfractions separated by affinity chromatography on concanavalin A-Sepharose. This finding was further substantiated by the nearly identical specific activities of some membrane-bound enzymes, Mg2+-ATPase, alkaline phosphatase and gamma-glutamyl transpeptidase. The specific activities of (Na+ + K+)-ATPase and of lysolecithin acyltransferase were several-fold enriched in fraction 2 compared to fraction 1, especially after rechromatography of fraction 1 on concanavalin A-Sepharose. Unseparated membrane vesicles contained two types of binding site for concanavalin A. In contrast, isolated subfractions showed a linear Scatchard plot; fraction 2 exhibited fewer binding sites for concanavalin A: the association constant was, however, 3.5-times higher than that measured in fraction 1. When plasma membranes isolated from concanavalin A-stimulated lymphocytes were separated by affinity chromatography, the yield of the two subfractions was similar to that of membranes from unstimulated lymphocytes. Upon stimulation with concanavalin A, Mg2+-ATPase, gamma-glutamyl transpeptidase and alkaline phosphatase were suppressed in their activities in both membrane subfractions. In contrast, the specific activities of (Na+ + K+)-ATPase and lysolecithin acyltransferase were enhanced preferentially in the adherent fraction (fraction 2). The data suggest the existence of domains in the plasma membrane of lymphocytes which are formed by a spatial and functional coupling of receptors with high affinity for concanavalin A, and certain membrane-bound enzymes, implicated in the initiation of lymphocyte activation.
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PMID:Characterization of functional domains of the lymphocyte plasma membrane. 613 98

Recent advances in insulin secretion indicate that pertussis toxin abolishes the inhibition by alpha 2 adrenoceptor activation of insulin release by the pancreas. Pertussis toxin adenosine diphosphate (ADP) ribosylates an inhibitory guanine nucleotide-binding protein (Ni) involved in inhibition of adenylate cyclase. The decrease in cyclic adenosine monophosphate (AMP) by epinephrine may account for its inhibition of insulin release. Insulin interaction with its receptor results in an increase in the tyrosine protein kinase activity of the receptor. Second messengers for insulin are generated, hexose transport is accelerated, and a cyclic AMP-independent protein kinase is activated that phosphorylates at serinethreonine residues. The activity of membrane-bound enzymes such as adenylate cyclase and Ca2+-Mg2+-ATPase is affected. The relative importance of these effects of insulin in its regulation of cellular metabolism remains to be established.
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PMID:Insulin secretion and action. 614 90

Sarcoplasmic reticulum vesicles were preloaded with either 45Ca2+ or unlabeled Ca2+ X 45Ca2+ efflux and influx, together with phosphorylation of the membrane-bound Ca2+, Mg2+-ATPase, were determined in the presence of either ATP and ADP or acetyl phosphate. ATP induced 45Ca2+ efflux. This ATP-induced 45Ca2+ efflux depended on ADP, external Ca2+, and Mg2+. The Ca2+ concentration dependence of the efflux was quite similar to the Ca2+ concentration dependence of the ATP-induced 45Ca2+ influx and the enzyme phosphorylation. The rate of the efflux was proportional to the steady level of the phosphoenzyme. The affinity for free ADP in this efflux was extremely high, being in good agreement with the affinity for free ADP in the transphosphorylation from the phosphoenzyme to ADP. These results show that the ATP-induced 45Ca2+ efflux represents the Ca2+-Ca2+ exchange (between the external medium and the internal medium) mediated by the phosphoenzyme. In this exchange, Mg2+ was essential for the exposure of the bound Ca2+ of the phosphoenzyme to the internal medium. 45Ca2+ efflux and influx were also activated by acetyl phosphate. This acetyl phosphate-induced efflux required the external Ca2+. The Ca2+ concentration dependence of the efflux agreed closely with that of the enzyme phosphorylation by acetyl phosphate. Furthermore, the rate of the efflux was proportional to the steady level of the phosphoenzyme. These and other findings show that the acetyl phosphate-induced 45Ca2+ efflux represents the Ca2+-Ca2+ exchange mediated by the phosphoenzyme and further demonstrate the direct dissociation of Ca2+ from the Ca2+-bound phosphoenzyme to the external medium in this Ca2+-Ca2+ exchange. The rate of the acetyl phosphate-induced, phosphoenzyme-mediated Ca2+ efflux was much slower than that of the ATP-, ADP-induced, phosphoenzyme-mediated Ca2+ efflux. This is consistent with our previous conclusion that the Ca2+ binding site is partially occluded upon the phosphorylation of the enzyme.
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PMID:Ca2+-Ca2+ exchange catalyzed by the membrane-bound Ca2+, Mg2+-ATPase of sarcoplasmic reticulum vesicles. 614 90

Endoneurial sodium, potassium adenosine triphosphatase (Na+,K+-ATPase) and Mg2+-ATPase activities were determined in routine sural nerve biopsies from patients being evaluated for peripheral neuropathy. A significant reduction of endoneurial Na+,K+-ATPase and Mg2+-ATPase activities was shown in six sural nerve biopsies from patients with Tangier disease complicated by mononeuropathy multiplex or progressive axonal neuropathy. Peripheral nerve ATPase activities did not correlate with myelinated or unmyelinated nerve fiber densities in these biopsies. Other peripheral neuronal disorders with reduced endoneurial Na+,K+-ATPase and Mg2+-ATPase activities included severe vasculitic neuropathy, diabetic neuropathy, tomaculous neuropathy, and motoneuron disease. Such reduced levels of ATPase activity in peripheral nerve may relate to altered endoneurial lipid metabolism and impaired axoplasmic flow.
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PMID:Endoneurial ATPase activity in Tangier disease and other peripheral neuropathies. 615 83

Chlordecone (Kepone) is a close structural analog of mirex, but it differs considerably from mirex in toxic action. Chlordecone primarily produces neurotoxic symptoms such as tremors in humans and animals. As with other organochlorine pesticides, the mechanism of the toxic action of chlordecone is not completely understood. An attempt is made in this paper to review the effects of chlordecone on the membrane-bound adenosinetriphosphatases (ATPases) and related phenomena. Chlordecone is shown to be a potent inhibitor of ATPases in different tissue preparations of several species. The order of sensitivity of the ATPases tested to chlordecone was: oligomycin-sensitive (mitochondrial) Mg2+-ATPase greater than Na+,K+-ATPase greater than Ca2+-ATPase greater than oligomycin-insensitive Mg2+-ATPase. Compared to other tissues tested, brain Na+K+-ATPase and heart mitochondrial Mg2+-ATPase were more sensitive to chlordecone. Oligomycin-insensitive Mg2+-ATPase was the least affected enzyme. Membrane-bound Na+, K+-ATPase has been associated with catecholamine uptake processes, and inhibitors of this enzyme, such as ouabain, have been found to decrease catecholamine uptake. Chlordecone decreased the uptake of catecholamines by rat heart membranes in a dose-dependent manner. Various cellular processes such as catecholamine uptake are dependent for energy on ATP, and most of this ATP is produced in the mitochondria through oxidative phosphorylation. Oligomycin-sensitive Mg2+-ATPase is involved in this coupling process. Chlordecone inhibition of this enzyme may result in depletion of mitochondrial ATP. This chain of events suggest that chlordecone interacts with membrane ATPases and thus may impair various energy-dependent cellular processes.
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PMID:Interaction of chlordecone with biological membranes. 617 65

Chlordecone, a polycyclic chlorinated insecticide known as Kepone, inhibited the activities of (Na+-K+)ATPase and Mg2+-ATPase in rat brain synaptosomes. Altered pH and specific activity curves for both enzymes demonstrated significant inhibition by chlordecone in buffered acidic, neutral and alkaline pH ranges. Noncompetitive inhibition with respect to activation by ATP in the case of (Na+-K+)ATPase was indicated by altered Vmax values with no significant change in Km values at any pH studied, except at pH 9.5. Mg2+-ATPase was inhibited uncompetitively as evidenced by altered Vmax and Km values. The activities of both ATPase were decreased in the presence of chlordecone at higher temperatures. Activation energy (delta E) values were found to be decreased significantly in the presence of chlordecone at 37 degrees. Arrhenius plots of both ATPases preincubated with chlordecone were found to be nonlinear. In the presence of chlordecone, Vmax was decreased without significant change in Km values for (Na+-K+)ATPase at all temperatures, suggesting a noncompetitive type of inhibition. In the case of Mg2+-ATPase, similar noncompetitive type inhibition was obtained at 27 degrees but not at 32 and 37 degrees. The kinetic data in general suggest that the chlordecone inhibited (Na+-K+)ATPase noncompetitively and Mg2+-ATPase uncompetitively at all pHs and temperatures studied. The present data suggest that inhibition of (Na+-K+)ATPase and Mg2+-ATPase, the two membrane-bound enzymes in synaptosomes, by chlordecone is temperature dependent and pH independent.
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PMID:Effect of chlordecone on pH and temperature dependent substrate activation kinetics of rat brain synaptosomal ATPases. 619 30

The lipid composition and fluidity of plasma membranes have been studied at different stages of liver regeneration (4, 15 and 24 h after surgery). The phospholipid and fatty acid composition is not modified, whereas the cholesterol/phospholipid ratio is lower with respect to control membranes. The modification of the physical properties of the membranes has been studied directly by EPR analysis and indirectly by temperature dependence and cooperativity of some membrane-bound enzymes (Mg2+-ATPase, (Na+ + K+)-ATPase and 5'nucleotidase). Surgical operation or anaesthesia alone causes an early increase in fluidity; such an effect appears to be markedly reduced at a later stage. There seems to be a marked effect of regeneration on plasma membrane fluidity 15 h after partial hepatectomy when several parameters--surface fluidity, cholesterol/phospholipid ratio, and 5'-nucleotidase activity in the presence of concanavalin A -- are modified and indicate an increase in membrane fluidity. It is suggested that this modification of membrane properties could be related to the proliferative process.
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PMID:Plasma membrane changes associated with rat liver regeneration. 624 90

The activity of Mg2+-ATPase and Na+-K+-ATPase was measured in media of calcium concentrations ranging from 10(-9)M to 10(-3)M, with retinal homogenates from rat and rabbit. In both species calcium stimulated the Mg2+-ATPase and inhibited Na+-K+-ATPase. In the rat, activity of Na+-K+-ATPase fell by 75% as calcium was increased from 10(-8)M to 10(-7)M and reached 90% inhibition only at 10(-3)M. By contrast, the activity in the rabbit fell gradually to a 90% inhibited state, over the range 10(-8)M to 10(-3)M. Calcium activated the Mg2+-ATPase by a maximum of 50% in each species, at a concentration of 10(-8)M in the rat and over a broader concentration range between 10(-5)M and 10(-4)M in the rabbit. It is postulated that maintenance of intracellular calcium at low levels by the Ca2+-activated Mg2+-ATPase or other cellular mechanisms is essential for the activity of the membrane-bound Na+-K+-ATPase of the retina.
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PMID:Influence of calcium on retinal ATPases. 624 22


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