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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)

Concanavalin A inhibits the (Na+-K+)-ATPase activity of isolated rat-liver plasma membranes, while leaving the Mg2+-ATPase unaffected. Glucagon and cyclic AMP act supplementary to the lectin in the inhibition. The lectin effect is counteracted by insulin and L-epinephrine, and is completely abolished by the beta-adrenergic blocking agent propranolol. Results are discussed on the basis of the known interactions of concanavalin A with plasma membrane components, including its hormone-like action.
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PMID:Studies on plasma membranes. XXIII. Hormone-like action of concanavalin A on liver plasma membranes: inhibition of (Na+-K+)ATPase. 12 72

Transverse tubule membranes isolated from rabbit fast skeletal muscle contain a very active Mg2+-ATPase (ATP phosphohydrolase, EC 3.6.1.3). This enzyme is very sensitive to inactivation by most detergents. However, after solubilization with either lysolecithin or digitonin, the Mg2+-ATPase can be purified in active form. Using a combination of selective solubilization followed by lectin affinity chromatography, ion-exchange chromatography, and native gel electrophoresis, the Mg2+-ATPase has been purified to near homogeneity. A prominent band with molecular mass of 105 kDa is observed when the purified protein is analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified 105-kDa Mg2+-ATPase protein is not structurally similar to the sarcoplasmic reticulum Ca2+-ATPase protein, as evidenced by very different cyanogen bromide peptide maps and amino acid compositions. The structural dissimilarities are complemented by functional differences observed between the Ca2+- and Mg2+-ATPases, including differential susceptibility to proteases, chemical modification reagents, and inactivation by fluorescein isothiocyanate and vanadate. All these data taken together demonstrate that the Mg2+-ATPase is a unique protein with little, if any, structural similarity to the sarcoplasmic reticulum Ca2+-ATPase or to other related enzymes such as mammalian kidney (Na,K)-ATPase or gastric mucosal (H,K)-ATPase.
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PMID:Purification and characterization of the Mg2+-ATPase from rabbit skeletal muscle transverse tubule. 297 Apr 63

Treatment of liver plasma membranes with phospholipase A2 or high doses of concanavalin A enhances the activity of Mg2+ATPase assayed at temperatures greater than 30 degrees C. The effects of the two treatments are not additive. Both the removal of phospholipids and binding of the lectin increase the degree of polarization of fluorescence of the lipid-soluble fluorophores, diphenylhexatriene and beta-parinaric acid, suggesting that decreased lipid fluidity may activate Mg2+-ATPase. In fact modification of lipid fluidity by reconstitution of phospholipase-treated membranes with phosphatidylcholines of defined fatty acid composition or by addition of cis-vaccenic acid showed a strong inverse correlation between Mg2+ATPase activity and lipid fluidity as monitored by fluorescence polarization. However, despite the ability of concanavalin A to nonspecifically order membrane lipid, its effect on Mg2+ATPase is apparently not mediated in this manner because other enzyme-activating lectins such as Ricinus communis agglutinin and wheat germ agglutinin are without effect on lipid fluidity. The facts that lectins of lower valency than tetravalent native concanavalin A such as divalent succinyl concanavalin A are far less effective in activating the enzyme and that paraformaldehyde treatment also activates suggests that cross-linking of membrane proteins is responsible. Hence, the diminution in activity of this membrane enzyme due to the disordering effect of heat in the physiological temperature range can be counteracted by isothermally increasing the order of either membrane lipid or protein.
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PMID:Ordering of bulk membrane lipid or protein promotes activity of plasma membrane Mg2+ATPase. 610 59

Transbilayer movement, or flip-flop, of lipids across the endoplasmic reticulum (ER) is required for membrane biogenesis, protein glycosylation, and GPI anchoring. Specific ER membrane proteins, flippases, are proposed to facilitate lipid flip-flop, but no ER flippase has been biochemically identified. The glycolipid Glc 3Man 9GlcNAc 2-PP-dolichol is the oligosaccharide donor for protein N-glycosylation reactions in the ER lumen. Synthesis of Glc 3Man 9GlcNAc 2-PP-dolichol is initiated on the cytoplasmic side of the ER and completed on the lumenal side, requiring flipping of the intermediate Man 5GlcNAc 2-PP-dolichol (M5-DLO) across the ER. Here we report the reconstitution of M5-DLO flipping in proteoliposomes generated from Triton X-100-extracted Saccharomyces cerevisiae microsomal proteins. Flipping was assayed by using the lectin Concanavalin A to capture M5-DLOs that had been translocated from the inner to the outer leaflet of the vesicles. M5-DLO flipping in the reconstituted system was ATP-independent and trypsin-sensitive and required a membrane protein(s) that sedimented at approximately 4 S. Man 7GlcNAc 2-PP-dolichol, a higher-order lipid intermediate, was flipped >10-fold more slowly than M5-DLO at 25 degrees C. Chromatography on Cibacron Blue dye resin enriched M5-DLO flippase activity approximately 5-fold and resolved it from both the ER glycerophospholipid flippase activity and the genetically identified flippase candidate Rft1 [Helenius, J., et al. (2002) Nature 415, 447-450]. The latter result indicates that Rft1 is not the M5-DLO flippase. Our data (i) demonstrate that the ER has at least two distinct flippase proteins, each specifically capable of translocating a class of phospholipid, and (ii) provide, for the first time, a biochemical means of identifying the M5-DLO flippase.
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PMID:Distinct flippases translocate glycerophospholipids and oligosaccharide diphosphate dolichols across the endoplasmic reticulum. 1859 86

Caulobacter crescentus cells adhere to surfaces by using an extremely strong polar adhesin called the holdfast. The polysaccharide component of the holdfast is comprised in part of oligomers of N-acetylglucosamine. The genes involved in the export of the holdfast polysaccharide and the anchoring of the holdfast to the cell were previously discovered. In this study, we identified a cluster of polysaccharide biosynthesis genes (hfsEFGH) directly adjacent to the holdfast polysaccharide export genes. Sequence analysis indicated that these genes are involved in the biosynthesis of the minimum repeat unit of the holdfast polysaccharide. HfsE is predicted to be a UDP-sugar lipid-carrier transferase, the glycosyltransferase that catalyzes the first step in polysaccharide biosynthesis. HfsF is predicted to be a flippase, HfsG is a glycosyltransferase, and HfsH is similar to a polysaccharide (chitin) deacetylase. In-frame hfsG and hfsH deletion mutants resulted in severe deficiencies both in surface adhesion and in binding to the holdfast-specific lectin wheat germ agglutinin. In contrast, hfsE and hfsF mutants exhibited nearly wild-type levels of adhesion and holdfast synthesis. We identified three paralogs to hfsE, two of which are redundant to hfsE for holdfast synthesis. We also identified a redundant paralog to the hfsC gene, encoding the putative polysaccharide polymerase, and present evidence that the hfsE and hfsC paralogs, together with the hfs genes, are absolutely required for proper holdfast synthesis.
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PMID:Characterization of the Caulobacter crescentus holdfast polysaccharide biosynthesis pathway reveals significant redundancy in the initiating glycosyltransferase and polymerase steps. 1875 30