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)

Fodrin, a non-erythrocyte spectrin-like protein, has been purified from bovine brain and found to be phosphorylated by the cyclic AMP-dependent protein kinase with a maximal stoichiometry of 1.02 +/- 0.06 mol of phosphate/mol of fodrin dimer (n = 4). This phosphorylation was not affected by the presence of actin and calmodulin. The phosphorylation of fodrin was found to occur exclusively at serine residues on the beta subunit. Two-dimensional thin layer electrophoresis and chromatography of a tryptic digest of phosphorylated fodrin showed one major phosphopeptide and a few minor ones. We have previously reported that nonphosphorylated fodrin is capable of stimulating the smooth muscle actomyosin Mg2+-ATPase by 50-70% under a well-defined set of conditions such as a critical fodrin concentration and an optimal preincubation time (Wang, C., Ngai, P.K., Walsh, M.P., and Wang, J.H. (1987) Biochemistry 24, 1110-1117). We now report that phosphorylation of fodrin completely eliminates this stimulatory effect. However, phosphorylation of fodrin was able to compete with nonphosphorylated fodrin to result in the abolition of the stimulatory effect. Similarly, nonphosphorylated fodrin could overcome the inhibitory effect created by phosphorylated fodrin. The present results support the suggestion that the stimulation of the smooth muscle actomyosin Mg2+-ATPase by fodrin may be a physiological phenomenon and cyclic AMP may serve as a regulator for this effect.
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PMID:Effect of phosphorylation by cyclic AMP-dependent protein kinase on the smooth muscle actomyosin Mg2+-ATPase stimulatory activity of fodrin. 295 61

Smooth-muscle myosin purified as described by Persechini & Hartshorne [(1983) Biochemistry 22, 470-476] contains trace amounts of calmodulin and myosin light-chain kinase, which can be removed by Ca2+-dependent hydrophobic-interaction chromatography followed by calmodulin-Sepharose affinity chromatography. The resultant column-purified myosin exhibits properties similar to those of the non-purified myosin, e.g. actin activation of the Mg2+-ATPase requires Ca2+/calmodulin-dependent phosphorylation of the two 20 kDa light chains. However, unlike the non-purified myosin, the column-purified myosin undergoes a time-dependent transition to a form which no longer requires phosphorylation for actin activation of the myosin Mg2+-ATPase. This transition is identified as a time-dependent change in conformation of the column-purified myosin from a 10 S to 6 S form and is caused by slow oxidation of the column-purified myosin, since it could be prevented by storage under N2 and reversed by 5 mM-dithiothreitol.
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PMID:Purification of smooth-muscle myosin free of calmodulin and myosin light-chain kinase. Susceptibility to oxidation. 296 Mar 20

The effects of chloroquine on calmodulin (CaM)-related enzyme activities and the shape of human erythrocytes have been studied. It was found that the CaM activation of rat brain phosphodiesterase was abolished by the addition of chloroquine. CaM was included in the assay of phosphodiesterase activity at the concentration that gave half-maximal activation. The concentration of chloroquine that caused 50% inhibition of CaM stimulation of phosphodiesterase was 7 X 10(-5)M. The type of inhibition was competitive with respect to CaM. The CaM-stimulated Ca2+, Mg2+-ATPase in erythrocyte membrane was also inhibited by chloroquine, the 50% inhibitory concentration of which was about 2 X 10(-4)M. Its mode of action was also competitive with respect to CaM. The shapes of erythrocyte ghosts prepared by hypotonic hemolysis were examined in a solution consisting of 2 mM MgCl2, 154 mM NaCl and 10 mM Tris-HCl (pH 7.4); they were discocytic in the presence of 2 mM ATP and in its absence. They were converted to the invaginated form by the addition of chloroquine in the concentration range of 1 X 10(-4)-5 X 10(-4)M. This concentration is similar to that which caused the inhibition of CaM activation of Ca2+, Mg2+-ATPase.
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PMID:Inhibition of calmodulin stimulation of phosphodiesterase and Ca2+, Mg2+-ATPase activities and shape change of erythrocyte ghosts by chloroquine. 296 Mar 25

The actin-activated Mg2+-ATPase activity of dephosphorylated chicken gizzard myosin reconstituted with actin, tropomyosin, myosin light-chain kinase (MLCK) and calmodulin was inhibited completely by purealin, 20 microM, whereas the activity of the phosphorylated and dephosphorylated myosin was not affected. Purealin inhibited the phosphorylation of myosin light chains caused by MLCK and calmodulin (IC50, 5 microM). On the other hand, purealin had no effect on myosin phosphorylation induced by Ca2+ -independent MLCK. The calmodulin-stimulated phosphodiesterase activity was inhibited by purealin (IC50, 7 microM) at concentrations very close to those that inhibit myosin phosphorylation. Kinetic analysis revealed a competitive mode of inhibition of calmodulin-stimulated phosphodiesterase activity by purealin. These results suggest that purealin acts as a calmodulin antagonist in reconstituted actomyosin from chicken gizzard, resulting in inhibition of light chain phosphorylation and the actin-activated ATPase activity of myosin.
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PMID:The mechanism of inhibition of light-chain phosphorylation by purealin in chicken gizzard myosin. 296 81

Highly purified microvillar 110 kDa polypeptide-calmodulin (110K-cam) complex was confirmed to have ATPase activities characteristic of a myosin. The effect of F-actin on these activities was investigated. The Mg2+-ATPase is activated about 2-fold by F-actin in a dose-dependent fashion, whereas the K+-EDTA-ATPase is inhibited by greater than 90% by F-actin. These data provide evidence for a functional relationship between the ATPase activity of 110K-cam and its interaction with F-actin. They also extend the similarities between 110K-cam and myosin. The results suggest that higher cells contain in addition to myosin a second class of myosin-like molecules represented by 110K-cam.
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PMID:ATPase activity of the microvillar 110 kDa polypeptide-calmodulin complex is activated in Mg2+ and inhibited in K+-EDTA by F-actin. 296 14

Ca2+-stimulated Mg2+-dependent ATPase (Ca2+ + Mg2+-ATPase) stimulated by calmodulin, by partial proteolysis or by oleic acid in erythrocyte membranes was inhibited by various derivatives of the naturally occurring alkaloid berbamine. The ability of these derivatives to inhibit trypsin-activated Ca2+ + Mg2+-ATPase correlated well with their ability to inhibit the calmodulin-stimulated enzyme. Inhibition of the trypsin-activated Ca2+ + Mg2+-ATPase by O-4-(ethoxybutyl)berbamine (EBB) was competitive with respect to ATP. The Ki for inhibition was about 8 microM. These results suggest that the binding site of EBB on the activated Ca2+ + Mg2+-ATPase may bear structural similarity to that on calmodulin, and may be closely related to the ATP-binding site on the enzyme.
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PMID:The effect of berbamine derivatives on activated Ca2+-stimulated Mg2+-dependent ATPase in erythrocyte membranes. 296 23

To investigate possible abnormalities in erythrocyte membrane enzyme activities in the pharmacogenetic disorder MH, membrane ATPase activities have been examined in erythrocyte ghosts prepared from red blood cells of MHS and normal swine. While no differences were noted in Mg2+-ATPase activities, the (Na+, K+)-ATPase activity of MHS erythrocyte ghosts was less than that of normal ghosts. Ca2+-ATPase activity exhibited low- and high-affinity Ca2+-binding sites in both types of erythrocyte ghost. While the Km for Ca2+ was greater for normal than for MHS erythrocyte ghosts at the high-affinity Ca2+-binding site, the reverse was true at the low-affinity Ca2+-binding site. Irrespective of the type of calcium binding site occupied, the Vmax for normal erythrocyte ghost Ca2+-ATPase activity was greater than that for MHS ghosts. In the presence of calmodulin, there was now no difference between MHS and normal erythrocyte ghosts in either the Km for Ca2+ or the Vmax of the Ca2+-ATPase activity. To determine if the calcium pumping activity of intact MHS and normal pig erythrocytes differed, calcium efflux from the 45Ca-loaded erythrocytes was determined; this activity was significantly greater for MHS than for normal erythrocytes. Thus, the present study confirms that there are abnormalities in the membranes of MHS pig red blood cells. However, we conclude that these abnormalities are unlikely to result in an impaired ability of MHS erythrocytes to regulate their cytosolic Ca2+ concentration.
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PMID:Erythrocyte membrane ATPase and calcium pumping activities in porcine malignant hyperthermia. 296 54

The organochlorine pesticide DDT is a liver tumour promoter and a potent inhibitor of intercellular communication. Present knowledge of the mechanism by which DDT inhibits intercellular communication is limited but it has been suggested that increased intracellular free calcium induced by DDT could be of importance. As the effects of calcium are closely associated with the multifunctional protein calmodulin (CaM) in most cells the potential binding of DDT to CaM and subsequent effects on CaM-stimulated Ca2+/Mg2+-ATPase activity were studied. DDT inhibited CaM-stimulated Ca2+/Mg2+-ATPase activity and bound to CaM in a manner similar to established CaM-inhibitors. Subsequently an in vitro assay for measuring inhibition of metabolic cooperation between 6-thioguanine (TG)-sensitive and TG-resistant Chinese hamster (V79) cells was used to investigate the possible involvement of CaM in the regulation of intercellular communication. Calmidazolium (CzM), a potent CaM inhibitor, was tested alone or in combination with the tumour promoters 12-O-tetradecanoyl phorbol-13-acetate (TPA) or DDT known inhibitors of intercellular communication. The results showed that CzM alone was without effect with regard to inhibition of metabolic cooperation but potentiated the response induced by TPA, an effect not noticed with DDT. These results suggest different mechanisms of action of TPA and DDT on metabolic cooperation and support the hypothesis that with calcium CaM may be of importance for drug-induced inhibition of intercellular communication and tumour promotion.
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PMID:Calmodulin involvement in TPA and DDT induced inhibition of intercellular communication. 296 82

Ciliary activity is regulated by Ca2+ and cyclic nucleotides, but the molecular mechanisms of the regulation are unknown. We have tested the ability of Ca2+ and cyclic nucleotides to alter ciliary Mg2+-ATPase or to stimulate phosphorylation of axonemal dynein. Mg2+-ATPase activity in cilia and axonemes from Paramecium was stimulated 2-fold by micromolar Ca2+, but this Ca2+ sensitivity was lost upon solubilization of the dyneins from the axoneme. The Ca2+-sensitive component of ciliary Mg2+-ATPase activity was inhibited by the dynein inhibitors vanadate and Zn2+, but was insensitive to the calmodulin antagonists calmidazolium and melittin. Dynein activity in the high-salt extract from axonemes was also insensitive to calmidazolium. Calmodulin did not sediment with 22 S or 12 S dyneins on sucrose gradients containing Ca2+, but it did sediment in the region from 19 S to 14 S. Mg2+-ATPase activity in ciliary fractions was unaltered in the presence of cAMP or cGMP. However, polypeptides associated with the 22 S and 12 S dyneins, as well as proteins of 19 S, 15 S, and 8 S, were substrates for endogenous ciliary kinases. High molecular weight polypeptides that sedimented at 22 S and 19 S were phosphorylated in a cyclic nucleotide-stimulated manner.
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PMID:Regulation of axonemal Mg2+-ATPase from Paramecium cilia: effects of Ca2+ and cyclic nucleotides. 296 17

The influence of hyperglycemia on calmodulin-stimulated Ca2+-Mg2+-ATPase activity was studied in 20 diabetic subjects. A clear inverse relationship between short-term hyperglycemia as well as chronic hyperglycemia and calmodulin-stimulated Ca2+-Mg2+-ATPase activity could be demonstrated. Such a relationship could not be shown for basal enzyme activity.
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PMID:Influence of hyperglycemia on Ca2+-Mg2+ -ATPase of red blood cells from diabetic patients. 296 32


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