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

---

Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanisms through which Ca2+ mobilization in rat hepatocytes results in the loss of total activity of 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase [Zammit & Caldwell (1990) Biochem. J. 269, 373-379] were investigated. The loss of total activity was shown to be paralleled by an equal loss of immunoreactive HMG-CoA reductase protein after exposure of hepatocytes to optimal concentrations of vasopressin plus glucagon for 40 min. This loss of enzyme protein was due to an inhibition of enzyme synthesis; the rate of degradation was unaffected. Other Ca(2+)-mobilizing conditions (phenylephrine, glucagon, vasopressin added singly and A23187) also resulted in graded inhibition of synthesis of HMG-CoA reductase. These effects were accentuated by omission of Ca2+ from the cell incubation medium, suggesting that it is the depletion of an intracellular InsP3-sensitive pool of Ca2+ to which synthesis of HMG-CoA reductase is sensitive. In agreement with this we found that t-butylhydroxybenzoquinone, which inhibits the activity of the Ca(2+)-ATPase of the endoplasmic-reticular membrane, mimicked the action of Ca(2+)-mobilizing hormones. However, taurolithocholate, which transiently mobilizes Ca2+ from the same pool, was ineffective. All these effects on HMG-CoA reductase were accompanied by parallel inhibition of 35S incorporation from [35S]methionine into total protein, suggesting that inhibition of reductase synthesis formed part of a generalized response of the hepatocyte to Ca2+ mobilization. Inhibition of the rate of synthesis of HMG-CoA reductase was, however, more responsive to Ca2+ mobilization in the absence of added Ca2+ from the extracellular medium. The concentrations of vasopressin required to elicit the inhibition of synthesis of HMG-CoA reductase were of the same order as those that elicited activation of glycogen phosphorylase in hepatocytes.
...
PMID:Rapid decrease in the expression of 3-hydroxy-3-methylglutaryl-CoA reductase protein owing to inhibition of its rate of synthesis after Ca2+ mobilization in rat hepatocytes. Inability of taurolithocholate to mimic the effect. 195 35

The main characteristics of L-tyrosine (L-Tyr) uptake by B16/F10 malignant melanocytes are reported. This amino acid can be taken up by two systems, both of them being saturable. The first one would be system L. This system can be studied in cells preloaded with amino acids that are a good substrate for system L, such as L-methionine or L-tryptophan. The kinetic parameters for L-Tyr uptake by this transport system are Vm = 6.5 pmol L-Tyr/10(3) cells.min and Km around 130 microM. The second system, probably the system ASC, shows lower capacity but higher affinity than the former. This system can be detected only in cells previously depleted of amino acids, showing approximate kinetic values of Vm 0.05 pmol L-Tyr/10(3) cells.min and Km around 5 microM. It is shown that the increase in cell density yields a decrease in the rate of L-Tyr uptake by system L, but this increase does not affect the high affinity system, alpha-MSH does not affect significantly the L-Tyr uptake by both systems. 2-Amino bicyclo-(2,2,1)-heptane-2-carboxylic acid produces a remarkable inhibition of the rate of L-Tyr uptake, but alpha-methylaminoisobutyric acid does not affect the rate of transport of this amino acid. The absence of sodium produces a slight but reliable decrease in the rate of L-Tyr uptake, supporting the involvement of two different transport systems. The ionophores monensin and nigericin enhance the transport by system L, but this effect is suppressed by the presence of ouabain. This finding indicates that the (Na+ -K+)-ATPase is essential for the stimulating action of ionophores.(ABSTRACT TRUNCATED AT 250 WORDS)
...
PMID:Transport of L-tyrosine by B16/F10 malignant melanocytes: characterization of the process. 198 30

Recent studies have established the clinical efficacy of S-adenosyl-L-methionine (SAMe) in the treatment of cholestasis associated with hepatic diseases, pregnancy and the administration of estrogen-containing oral contraceptives. In 4 clinical trials involving a total of 639 patients with cholestasis due to acute or chronic liver disease, SAMe in an intravenous dose of 800 mg/day or an oral regimen of 1.6 g/day for 2 weeks was superior to placebo in relieving the symptom of pruritus and in restoring serum total bilirubin and serum alkaline phosphatase towards normal. The drug is also effective in intrahepatic cholestasis of pregnancy (ICP), with intravenous administration of 800 mg/day for 2 weeks producing a substantial reduction in pruritus and an improvement in abnormal liver function indices. Moreover, SAMe treatment decreases the incidence of premature labour. SAMe appears to be the first safe and effective approach to the treatment of this syndrome, and also protects against the adverse hepatic effects of small doses of estrogen in patients with a history of ICP by normalising liver biochemistry and the oversaturated biliary lipid composition of the gallbladder bile. In animal models, SAMe reverses the pathological liver changes induced by xenobiotics such as taurolithocholate and alpha-naphthyl-isothiocyanate (ANIT) and the antipsychotic chlorpromazine. Several cooperative mechanisms appear to underlie the anticholestatic action of SAMe, the most important being the restoration of normal hepatocyte membrane fluidity and Na+, K+ ATPase activity, through a reversal of the reduction in phospholipid methylation produced by hepatotoxic agents. In addition, SAMe may act by promoting trans-sulphuration pathway reactions and consequently improving the detoxifying capacity of this metabolic system.
...
PMID:Role of S-adenosyl-L-methionine in the treatment of intrahepatic cholestasis. 208 76

The major biological functions of S-adenosyl-L-methionine (SAMe) include methylation of various molecules (transmethylation) and synthesis of cysteine (trans-sulphuration). A stable double salt of SAMe has been found to be effective in intrahepatic cholestasis. The mechanism of its therapeutic effect is not fully understood but presumably involves methylation of phospholipids. Methylation of plasma membrane lipids may affect membrane fluidity and viscosity, which modulate the activities of a number of membrane-associated enzymes, for example, the activity of enzymes involved in Na+/Ca++ exchange (e.g. sarcolemmal vesicles), Na+/K+ adenosine triphosphatase (ATPase) [e.g. hepatocyte plasma membranes], and Na+/H+ exchange (e.g. plasma membranes of colonic cells). Recently, patients with cirrhosis were shown to have an acquired metabolic block in the hepatic conversion of methionine to SAMe. These patients, when administered conventional elemental diets, develop abnormally low plasma concentrations of cysteine and choline, 2 nonessential nutrients present in low concentrations in most elemental diets. These low concentrations probably reflect systemic deficiencies attributable to reduced endogenous syntheses of cysteine and choline caused by limited availability of hepatic SAMe. Such cirrhotic patients are often in negative nitrogen balance and have abnormal hepatic functions, which are corrected by cysteine and choline supplements. Noncirrhotic patients on parenteral elemental diets also become deficient in cysteine and choline. Consequently, these patients may require SAMe as an essential nutrient to normalise their overall hepatic transmethylation and trans-sulphuration activities.
...
PMID:Biochemistry and pharmacology of S-adenosyl-L-methionine and rationale for its use in liver disease. 208 85

The amino-terminal region of muscle tropomyosin is highly conserved among muscle and 284-residue non-muscle tropomyosins. Analysis of fusion and nonfusion striated alpha-tropomyosins and a mutant in which residues 1-9 have been deleted has shown that the amino terminus is crucial for function. The presence of 80 amino acids of a nonstructural influenza virus protein (NS1) on the amino terminus of tropomyosin allows magnesium-independent binding of tropomyosin to actin. The fusion tropomyosin inhibits the actomyosin S1 ATPase at all myosin S1 concentrations tested, indicating that the presence of the fusion peptide prevents myosin S1 from switching the actin filament from the inhibited to the potentiated state. Nonfusion tropomyosin, an unacetylated form, has no effect on the actomyosin S1 ATPase, though it regulates normally with troponin. Deletion of residues 1-9, which are believed to overlap with the carboxyl-terminal end of tropomyosin in the thin filament, results in loss of tropomyosin function. The mutant is unable to bind to actin, in the presence and absence of troponin, and it has no regulatory function. The removal of the first 9 residues of tropomyosin is much more deleterious than removal of the last 11 by carboxypeptidase digestion. We suggest that the structure of the amino-terminal region and acetylation of the initial methionine are crucial for tropomyosin function.
...
PMID:The amino terminus of muscle tropomyosin is a major determinant for function. 213 42

Phosphatidylethanolamine N-methylation was examined in cardiac subcellular membranes after inducing chronic experimental diabetes in rats (65 mg streptozotocin/kg, i.v.). The incorporation of radiolabeled methyl groups from S-adenosyl-L-methionine in diabetic sarcolemma was significantly depressed at all three catalytic sites (I, II, and III) of the methyltransferase system. An increase in methyl group incorporation was evident at site I without any changes at sites II and III in diabetic sarcoplasmic reticulum and mitochondria. Similar changes were also seen for the individual N-methylated lipids (monomethyl-, dimethylphosphatidylethanolamine, and phosphatidylcholine) specifically formed at each catalytic site in all cardiac membranes from diabetic animals. These alterations in N-methylation were reversible by a 14-d insulin therapy to the diabetic animals. In the presence of 10 microM ATP and 0.1 microM Ca2+, N-methylation was maximally activated at site I in both control and diabetic sarcolemma and sarcoplasmic reticulum, but not in mitochondria. Incubation of cardiac membranes with of S-adenosyl-L-methionine showed that Ca2(+)-stimulated ATPase activities in both sarcolemma and sarcoplasmic reticulum were augmented; however, the activation of diabetic sarcolemma was lesser and that of diabetic sarcoplasmic reticulum was greater in comparison with the control preparations. These results identify alterations in phosphatidylethanolamine N-methylation in subcellular membranes from diabetic heart, and it is suggested that these defects may be crucial in the development of cardiac dysfunction in chronic diabetes.
...
PMID:Alterations in phospholipid N-methylation of cardiac subcellular membranes due to experimentally induced diabetes in rats. 214 1

VMA3, a structure gene of the vacuolar membrane H(+)-ATPase subunit c of Saccharomyces cerevisiae, has been cloned and characterized. The VMA3 gene encodes a hydrophobic polypeptide with 160 amino acids as reported previously by Nelson and Nelson (Nelson, H., and Nelson, N. (1989) FEBS Lett. 247, 147-153). Peptide sequence analysis indicated that the VMA3 gene product lacks N-terminal methionine and does not have a cleavable signal sequence. To investigate functional and structural roles of the subunit c for vacuolar acidification and protein transport to the vacuole, haploid mutants with the disrupted VMA3 gene were constructed. The vma3 mutants can grow in nutrient-enriched medium, but they have completely lost the vacuolar membrane H(+)-ATPase activity and the ability of vacuolar acidification in vivo. The subunit c was found to be indispensable for the assembly of subunits a and b of the H(+)-ATPase complex. The disruption of the VMA3 gene causes yeast cells with considerable lesions in vacuolar biogenesis and protein transport to the vacuole and inhibits endocytosis of lucifer yellow CH completely.
...
PMID:Roles of the VMA3 gene product, subunit c of the vacuolar membrane H(+)-ATPase on vacuolar acidification and protein transport. A study with VMA3-disrupted mutants of Saccharomyces cerevisiae. 214 83

Parathyroid hormone (PTH) has been shown to bind specifically to the beta subunit of the mitochondrial ATPase on nitrocellulose blots. We have now examined this interaction further, using intact mitochondria, submitochondrial particles, and the purified F1 ATPase. With intact mitochondria, 1 microM concentrations of PTH and its biologically active 1-34 fragment activate the ATPase about 3-fold. This effect was reduced to a 1.4-fold activation with 3-34 and 7-34 fragments of the hormone, and oxidized PTH gave no detectable activity. Activation could only be observed below pH 7. PTH had no significant effect on the activity of the purified enzyme or on submitochondrial particles. However, specific binding of an iodinated PTH analog, [Nle 8,18-Tyr 34] bPTH (1-34) amide, was found with submitochondrial particles and the purified ATPase. Binding affinity with the purified enzyme was about 10(-3) that of the plasma membrane receptor, and the molar stoichiometry was close to 1:1 (PTH:intact enzyme). With submitochondrial particles the affinity was about 10-fold higher than with the purified enzyme. This binding was further examined with PTH derivatives and fragments, and compared to that seen in the plasma membrane receptor. Oxidation of methionine 18 in PTH reduced the affinity about 50%, oxidation of methionine 8 reduced the affinity 95%, and oxidation of both methionines further decreased affinity in both membranes and submitochondrial particles. However, when compared to the native hormone, the 3-34 and 7-34 PTH fragments had much higher affinity for the submitochondrial particles than for the plasma membranes. PTH also reduced chemical crosslinking of the ATP analog, p-fluorosulfonyl benzoyl 5'-adenosine, to the alpha subunit of this enzyme, but did not alter labeling of the enzyme with 3'-O-(4'-benzoyl) benzoyl ATP, suggesting that the hormone binds near a regulatory nucleotide binding site. Direct chemical crosslinking of PTH to the beta-subunit of the enzyme was attained with a cleavable, photoactivate crosslinker, sulfosuccinimidyl 2-(p-azidosalicylamido) ethyl-1,3-dithiopropionate. The crosslinked protein was cleaved with cyanogen bromide and the labeled fragments were sequenced. The labeled fragments were found to be segments of the protein which have previously been implicated as being close to the noncatalytic ATP binding sites.
...
PMID:Characterization of the interaction of parathyroid hormone with the mitochondrial ATPase. 214 4

Scallop adductor myosin is regulated by its subunits; the regulatory light chain (R-LC) and essential light chain (E-LC). Myosin light chains suppress muscle activity in the absence of calcium and are responsible for relaxation. The binding of Ca2+ to the myosin triggers contraction by releasing the inhibition imposed on myosin by the light chains. To map the functional domains of the R-LC, we have carried out mutagenesis followed by bacterial expression. Both wild-type and mutant proteins were hybridized to scallop myosin heavy chain/E-LC to map the regions of the light chain that are responsible for the binding to the myosin heavy chain/E-LC, for restoring the specific calcium-binding site, and controlling the myosin ATPase activity. The R-LC is expressed in Escherichia coli using the pKK223-3 (Pharmacia) expression vector and has been purified to greater than 90% purity. E. coli-expressed wild-type R-LC differs from the native R-LC by having the initiating methionine residue and an unblocked NH2 terminus. The wild-type R-LC restores Ca2+ binding and Ca2+ sensitivity when hybridized to scallop myosin. A point mutation of the sixth Ca2(+)-liganding position of domain I (Asp39----Ala39) results in a R-LC that binds more weakly to the heavy chain/E-LC and restores the specific Ca2(+)-binding site but not regulation of the actin-activated Mg2+ ATPase. A second mutation was produced by substituting the last 11 residues of the COOH terminus with 15 different residues. This mutant restores the specific Ca2(+)-binding site, but does not restore Ca2+ regulation to the actin-activated ATPase activity. Several other point mutations do not alter light chain function. The experiments directly establish that the divalent cation-binding site of domain I is functionally distinct from the specific Ca2(+)-binding site. The results indicate that an intact domain I and the COOH terminus are required to suppress the myosin ATPase activity. The fact that the domain I mutation and the COOH-terminal mutation disrupt regulation but do not affect Ca2(+)-binding indicates that these two aspects of regulation are separable and, therefore, the R-LC has distinct functional regions.
...
PMID:Regulation of scallop myosin by mutant regulatory light chains. 214 99

Point mutations of Asp-376 of the alpha-subunit of Torpedo californica Na+/K(+)-ATPase (the site of phosphorylation during the catalytic cycle) to Asn, Glu or Thr led to virtual abolishment of Na+/K(+)-ATPase activity and ouabain-binding capacity. Replacement of Lys-507 of the same subunit (the putative ATP-binding site) by Met resulted in decreases in Na+/K(+)-ATPase activity and ouabain-binding capacity. These results are in agreement with those reported for rabbit sarcoplasmic reticulum Ca2(+)-ATPase (Maruyama, K. and MacLennan, D.H. (1988) Proc. Natl. Acad. Sci. USA 85, 3314-3318).
...
PMID:Site-directed mutagenesis of Asp-376, the catalytic phosphorylation site, and Lys-507, the putative ATP-binding site, of the alpha-subunit of Torpedo californica Na+/K(+)-ATPase. 215 58


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---