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)

We have investigated the localization of a set of intrinsic ATPase activities associated with purified synaptic plasma membranes and consisting of (a) a Mg2+-ATPase; (b) an ATPase active at high concentrations of Ca2+ in the absence of Mg2+ (CaH-ATPase); (c) a Ca2+ requiring Mg2+-dependent ATPase (Ca + Mg)-ATPase, stimulated by calmodulin (Ca-CaM-ATPase); (d) a Ca2+-dependent ATPase stimulated by dopamine (DA-ATPase); and (e) the ouabain-sensitive (Na + K)-ATPase. The following results were obtained: (1) All ATPases are largely confined to the presynaptic membrane; (2) the DA-, (Ca + Mg)-, (Ca-CaM)-, and (Na + K)-ATPases are oriented with their ATP hydrolysis sites facing the synaptoplasm; (3) the Mg- and CaH-ATPases are oriented with their ATP hydrolysis sites on the junctional side of the presynaptic membrane and are therefore classified as ecto-ATPases of as yet unknown function.
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PMID:Localization of endogenous ATPases at the nerve terminal. 629 99

The effect of calcium on ATP-phosphohydrolase activity of rat brain homogenates has been investigated. In both the presence and absence of the chelating agent EDTA, free calcium within the concentration range 1.2 x 10(-7) to 5.0 x 10(-4) moles/l consistently affected only the activity of Na+, K+-ATpase; the activities of Mg2+-ATPase and Na+-ATPase were essentially unchanged by Ca2+; Ca2+-ATPase could not be demonstrated. In either the presence or absence of EDTA, concentrations of free-Ca2+ above 3 x 10(-6) moles/l caused an inhibition of Na+,K+-ATPase activity. In the presence of EDTA, concentrations of free-Ca2+ below 3 x 10(-6) moles/l were ineffective at altering Na+, K+-ATPase activity but, in the absence of EDTA, free-Ca2+ in this concentration range caused a marked stimulation of the enzyme. Evidence is presented to show that the stimulation of Na+, K+-ATPase by calcium is modulated by the regulatory protein calmodulin. Since the stimulation occurs over the range of concentrations at which calcium would be expected to be encountered within the cell, it is suggested that this is the major physiological effect of calcium on Na+, K+-ATPase.
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PMID:Stimulation of neuronal Na+, K+-ATPase by calcium. 630 54

In previous work from this laboratory, a partially purified protein kinase from the soil amoeba Acanthamoeba castellanii was shown to phosphorylate the heavy chain of the two single-headed Acanthamoeba myosin isoenzymes, myosin IA and IB, resulting in a 10- to 20-fold increase in their actin-activated Mg2+-ATPase activities (Maruta, H., and Korn, E.D. (1977) J. Biol. Chem. 252, 8329-8332). A myosin I heavy chain kinase has now been purified to near homogeneity from Acanthamoeba by chromatography on DE-52 cellulose, phosphocellulose, and Procion red dye, followed by chromatography on histone-Sepharose. Myosin I heavy chain kinase contains a single polypeptide of 107,000 Da by electrophoretic analysis. Molecular sieve chromatography yields a Stokes radius of 4.1 nm, consistent with a molecular weight of 107,000 for a native protein with a frictional ratio of approximately 1.3:1. The kinase catalyzes the incorporation of 0.9 to 1.0 mol of phosphate into the heavy chain of both myosins IA and IB. Phosphoserine has been shown to be the phosphorylated amino acid in myosin IB. The kinase has highest specific activity toward myosin IA and IB, about 3-4 mumol of phosphate incorporated/min/mg (30 degrees C) at concentrations of myosin I that are well below saturating levels. The kinase also phosphorylates histone 2A, isolated smooth muscle light chains, and, to a very small extent, casein, but has no activity toward phosvitin or myosin II, a third Acanthamoeba myosin isoenzyme with a very different structure from myosin IA and IB. Myosin I heavy chain kinase requires Mg2+ but is not dependent on Ca2+, Ca2+/calmodulin, or cAMP for activity. The kinase undergoes an apparent autophosphorylation.
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PMID:Purification and characterization of a myosin I heavy chain kinase from Acanthamoeba castellanii. 630 72

Soluble myosin heavy chain kinases (MHC kinases) were partially purified from growth phase and aggregation-competent cells of Dictyostelium discoideum. In the aggregation-competent cells, two MHC kinases were distinguishable. One of these enzymes, called MHC kinase II, was inactivated by Ca2+ and calmodulin in a highly temperature-dependent reaction. A MHC kinase found in growth phase cells did not have these regulatory properties. Substrate specificities were analysed for MHC kinase II and for the MHC kinase from growth phase cells. Both enzymes phosphorylated threonine residues of the myosin heavy chains of D. discoideum and Physarum polycephalum. Phosphopeptide mapping of D. discoideum myosin and determination of the stoichiometry of its phosphorylation suggested the presence of two phosphorylation sites per heavy chain. Both sites were contained within a 38-kd chymotryptic fragment. The inactivation of MHC kinase II by Ca2+ plus calmodulin suggests this enzyme has a role in the regulation of myosin functions during the chemotactic response of a cell. The phosphorylated myosin had about one third the actin-activated Mg2+-ATPase activity of the non-phosphorylated myosin. Previous findings indicated that stimulation of D. discoideum cells with the chemo-attractant cAMP increases the cytoplasmic Ca2+ concentration. Under these conditions MHC kinase II might be inhibited and the dephosphorylated, more active form of myosin would accumulate.
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PMID:Myosin heavy chain kinase inactivated by Ca2+/calmodulin from aggregating cells of Dictyostelium discoideum. 631 44

A 20-kDa protein becomes phosphorylated in a process stimulated by Ca2+ and calmodulin in the light microsomal fraction of rat liver homogenate. The uptake of Ca2+ in light microsomal fraction is also calmodulin-stimulated. The stimulation of Ca2+ transport is associated with the operation of a protein phosphorylation system dependent on Ca2+ and calmodulin. Transport is inhibited by a protein phosphatase which is stimulated by Ca2+ and calmodulin. It is proposed that the phosphorylation of the 20-kDa protein, which is stimulated by Ca2+ and calmodulin, plays a role in the regulation of the microsomal Ca2+, Mg2+-ATPase.
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PMID:Calmodulin-dependent protein phosphorylation and calcium uptake in rat-liver microsomes. 632 3

A kinetic model was proposed to simulate an isometric contraction curve in smooth muscle on the basis of the myosin phosphorylation hypothesis. The Ca2+-calmodulin-dependent activation of myosin light-chain kinase and the phosphorylation-dephosphorylation reaction of myosin were mathematically treated. Solving the kinetic equations at a steady state, we could calculate the relationship between the Ca2+ concentration and the myosin phosphorylation. Assuming that two-head-phosphorylated myosin has an actin-activated Mg2+-ATPase activity and that this state corresponds to an active state, we computed the time courses of the myosin phosphorylation and the active state for various Ca2+ transients. The time course of the active state was converted into that of isometric tension by use of Sandow's model composed of a contractile element and a series elastic component. The model could simulate not only the isometric contraction curves for any given Ca2+ transient but also the following experimental results: the calmodulin-dependent shift of the Ca2+ sensitivity of isometric tension observed in skinned muscle fibers, the disagreement between the Ca2+ sensitivity of myosin phosphorylation and that of isometric tension at a steady state, and the disagreement between the time course of myosin phosphorylation and that of isometric tension development.
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PMID:Kinetic model for isometric contraction in smooth muscle on the basis of myosin phosphorylation hypothesis. 654 23

The association of calmodulin with brain synaptic vesicle proteins was analyzed. Scatchard analysis of [125I]calmodulin binding to brain synaptic vesicles revealed one high-affinity, low-binding-capacity, Kd = 1.0 (+/- 0.15) nM, Bmax = 4.1 (+/- 0.6) pmol/mg, and one low-affinity high-binding-capacity site, Kd = 177. (+/- 12.0) nM and Bmax = 202 (+/- 15.0) pmol/mg. Triton X-100 solubilization of synaptic vesicle proteins and subsequent elution on a Sepharose-4B-CNBr-calmodulin affinity column demonstrated that two protein doublets of approximate MrS 55 K and 30 K were the major synaptic vesicle calmodulin binding proteins. In addition there were two minor calmodulin binding singlet polypeptides with MrS 62 K and 40 K. Calmodulin stimulated endogenous synaptic vesicle protein kinase, Ca2+, Mg2+-ATPase and Ca2+ uptake activities. Phosphorylation assays coupled with immunological studies using affinity-purified antibodies suggested that the synaptic vesicle Ca2+/calmodulin-dependent protein kinase migrated in the 30 K Mr region.
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PMID:Preliminary characterization of synaptic vesicle/calmodulin interaction. 683 73

Calmodulin was isolated as an electrophoretically homogeneous protein from bovine posterior pituitary glands. The yield indicated that this gland is a particularly rich source. Purified bovine posterior pituitary calmodulin and bovine brain calmodulin had identical electrophoretic mobilities on 10% and 12% polyacrylamide gels. The protein was further identified by molecular weight determination and by amino acid analysis which showed that it contained trimethyllysine, one residue per molecule. Bovine posterior pituitary calmodulin was found to activate a preparation of calmodulin-deficient phosphodiesterase from bovine heart. In addition, pituitary calmodulin stimulated Ca+ + Mg2+-ATPase activity associated with a purified nerve ending plasma membrane fraction. This dependence could only be demonstrated after successive washing of the membranes with EGTA buffers, a procedure designed to remove endogenous calmodulin.
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PMID:Purification and characterization of posterior pituitary calmodulin and its activation of neurosecretosome Ca2+ + Mg2+-ATPase activities. 711 92

The relationship between adenylate cyclase activity in the synaptic membrane fraction (M1) of rat brain and lipid peroxidation of these membranes was examined. In the presence of 5 mM dithiothreitol (DTT), 1 to 10 microM Fe/+ activated adenylate cyclase 2- to 4-fold. Of several metal ions, Fe2+ was the most effective. Other enzymes in M1, such as Mg2+-ATPase, (Na+-K+)-ATPase, 5'-nucleotidase, acetylcholinesterase, and phosphodiesterase, were not activated by Fe2+ plus DTT. Activation of adenylate cyclase by Fe2+ plus DTT was accompanied by production of malondialdehyde, a product of lipid peroxidation. Formation of malondialdehyde was completely parallel with enzyme activation. Ascorbic acid or a NADPH system also stimulated enzyme activity and caused lipid peroxidation. Activation of the enzyme and lipid peroxidation induced by Fe2+ plus DTT, ascorbic acid, or NADPH was completely prevented by simultaneous addition of N,N'-diphenyl-p-phenylenediamine, an inhibitor of lipid peroxidation. This inhibitor also prevented the decrease in turbidity of the enzyme preparation induced by Fe2+ plus DTT. The stimulatory effects of NaF, guanylyl-5'-imidodiphosphate and calmodulin, respectively, and that of Fe2+ plus DTT on the enzyme activity were additive. Activation of adenylate cyclase by Fe2+ plus DTT was only observed in brain synaptic membranes, not in erythrocyte ghosts, liver plasma membranes, or cardiac sarcolemma. These results indicate that lipid peroxidation of synaptic membranes was accompanied by specific stimulation of adenylate cyclase activity.
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PMID:Activation of adenylate cyclase of rat brain by lipid peroxidation. 721 51

Calcium homeostasis in synaptosomes is altered during aging. The intrasynaptomal free calcium concentration ([Ca2+]i) was determined in 3- and 24-month-old rats treated with or without Rb1 and Rg1. As expected, the [Ca2+]i level increased with age. Treatment with Rbl and Rgl elicited an obvious decrease of [Ca2+]i content, especially in aged rates. In addition, Rb1 and Rgl significantly stimulated the activity of Na+, K+-ATPase while Rbl inhibited the activity of Ca2+, Mg2+-ATPase and calmodulin. In view of the close relationship of [Ca2+]i level with aging, the changes of [Ca2+]i induced by Rbl and Rgl, as shown by our results, might provide an explanation of the mechanisms of their antiaging function.
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PMID:Effects of ginsenoside Rb1 and Rg1 on synaptosomal free calcium level, ATPase and calmodulin in rat hippocampus. 755 76


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