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

Activation of membrane-associated thiamin triphosphatase from rat brain requires a divalent cation (Mg2+, Ca2+, or Mn2+). The optimum concentration of Mg2+ necessary for maximal enzyme activity varies with substrate concentration; conversely, the maximal rate of hydrolysis attainbale by increasing thiamin triphosphate concentration is directly proportional to [Mg2+] for all levels of Mg2+ below that of the substrate. Under appropriate conditions, the Km of the thiamin triphosphatase for Mg2+ and for thiamin triphosphate are shown to be identical. Dissociation constants (Kd) for the binding of Mg2+ to thiamin triphosphate, thiamin diphosphate, and thiamin were determined; kinetic data re-expressed in terms of [Mg2+-thiamin triphosphate] conform to simple single substrate predictions, suggesting that the true enzyme substrate may be the Mg2+-thiamin triphosphate complex. Excess free Mg2+ inhibits thiamin triphosphatase activity competitively while excess free thiamin triphosphate in concentrations up to 10 times Km has no effect on the membrane-bound enzyme.
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PMID:Membrane-associated thiamin triphosphatase. II. Activation by divalent cations. 17 10

The elongation factor 1- and elongation factor 2-dependent GTPase (guanosine triphosphatase) activities of ribosomes are inhibited by ricin, a toxic protein known to inactivate the 60S ribosomal subunit. It is suggested that also in eukaryotic ribosomes a "GTPase site', located on the larger subunit, is common to the two elongation factors.
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PMID:Relationship between elongation factor I- and elongation factor II- dependent guanosine triphosphatase activities of ribosomes. Inhibition of both activities by ricin. 17 82

Electron microscopic cytochemistry was used to determine the localization of five phosphatase enzymes-glucose-6-phosphatase, inosine diphosphatase, thiamine pyrophosphatase, acid phosphatase, and adenosine triphosphatase-in control human testes. Glucose-6-phosphatase occurred in the endoplasmic reticulum and nuclear envelope of Sertoli cells, Leydig cells and primitive spermatogonia, but was not observed in more advanced spermatogenic cells. The presence of glucose-6-phosphatase activity paralleled the presence of glycogen in spermatogenic cells, i.e., both occurred in type AL and AD spermatogonia but not in type AP or B spermatogonia or in more advanced spermatogenic cells. Inosine diphosphatase activity was found in the endoplasmic reticulum, nuclear envelope, and Golgi complex of Sertoli cells and all spermatogenic cells except late spermatids. Additionally, inosine diphosphatase activity was localized at the junctions between Sertoli cells and late spermatids, but was not associated with any other plasma membrane. Thiamine pyrophosphatase reaction product was found in the Golgi bodies of Sertoli cells and in spermatogenic cells through immature spermatids. Neither inosine diphosphatase nor thiamine pyrophosphatase was observed in the Golgi bodies of spermatids during acrosomal formation. Acid phosphatase activity was found in lysosomes of spermatogonia, spermatocytes, and spermatids, in lysosomes of Leydig cells, and in lysosomes, lipofuscin bodies, and Golgi cisternae of Sertoli cells. It is thought that Sertoli lysosomes play a role in the phagocytosis of degenerating germ cells; however, the role of spermatogenic or Leydig lysosomes is unknown. Adenosine triphosphatase activity occurred at the interfaces between two spermatogonia, and between Sertoli cells and spermatogonia, but was not observed in the spaces between two Sertoli cells, two spermatocytes, two spermatids, or between Sertoli cells and spermatocytes, or between Sertoli cells and spermatids.
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PMID:The fine structural localization of testicular phosphatases in man: the control testis. 17 58

The nucleoside triphosphatase [EC 3.6.1.15] activity of actomysin and that of myosin are measured by varying the concentration of nucleoside triphosphate and that of CaCl2 or MgGl2. The results thus obtained are examined by asking a question of which is responsbile for the activity, the true substrate and the active enzyme in terms of the reaction scheme shown in p. 719. The answers found for the above question are summarized in Table I (see p. 720). It is emphasized that the summmary (Table I) corresponds very well to the fact that myosin alone does not superprecipitate in the presence of either calcium or magnesium ions, whereas actomyosin does superprecipitate in the presence of magnesium ions and not in the presence of calcium ions. Obviously, the true substrate type of reaction scheme represents a kinetic property characteristic of the superprecipitation-coupled nucleoside-triphosphatase. It is also noted of the summary (Table I) that actin is capable of not only activating Mg-nucleoside-triphosphatase but also switiching the reaction scheme from the active enzyme type to the true substrate type. It is known that trinitrophenylation of myosin results in activation of the Mg-ATPase activity of myosin. However, it is now found that trinitrophenylation is not capable of switiching the reaction scheme, that is to say that the Mg-ATPase reaction of trinitrophenyl-myosin stays with the active enzyme type of reaction scheme and that of acto-trinitrophenyl-myosin with the true substrate type of reaction scheme. Effect of actin on the function of myosin seems, therefore, very unique.
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PMID:A new kinetic property characteristic of the actomyosin-nucleoside-triphosphatase. 17 88

Adenosine triphosphatase (ATPase) activity in erythrocyte membranes from patients with Duchenne dystrophy was inhibited by ouabain less than in normal individuals in assay systems containing high or low contents of salt. Epinephrine and cyclic adenosine monophosphate increased total ATPase activity in all samples, and epinephrine restored ouabain sensitivity to the Duchenne membranes. Basal adenyl cyclase activity in about twice that of controls. Epinephrine stimulated adenyl cyclase activity of normal membranes two to three times, but did not stimulate the enzyme in Duchenne membranes. These differences may reflect a genetic abnormality of the membrane.
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PMID:Biochemical abnormalities of erythrocyte membranes in Duchenne dystrophy. Adenosine triphosphatase and adenyl cyclase. 18 Sep 37

When photosynthetic membranes from Rhodospirillum rubrum, devoid of loosely bound small molecules and proteins, were passed through a French-pressure cell, the enzyme adenosine-5'-triphosphatase (EC 3.6.1.3.) (ATPase) was released into the soluble fraction. The solubilized ATPase was purified to homogeneity. In many respects it behaved like the enzyme purified by other workers, but it also hydrolyzed Mg-ATP with a small, but significant rate. Furthermore, it was much more stable. Maximal restoration of photophosphorylation in ATPase-depleted membranes was achieved by addition of about 1 mg purified ATPase per mg bacteriochlorophyll. For reconstitution of NAD+-photoreduction, about half of this amount was saturating.
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PMID:Coupling factor adenosine-5'-triphosphatase from Rhodospirillum rubrum: a simple and rapid procedure for its purification. 18 8

A rat liver nuclear envelope fraction isolated essentially by the technique of Monneron et al. (J. Cell Biol. 55, 104-125 (1972) is characterized by high levels of glucose-6-phosphatase and 5'-nucleotidase. A broadly specific nucleoside triphosphatase activity is present. Cytochromes b5 and P-450 as well as NADPH- and NADH-cytochrome c reductase activities are present but at lower levels than found in microsomes. Cytochrome c oxidase activity is low. RNA polymerase activity is absent from the nuclear envelope fraction. Cytochemistry shows that glucose-6-phosphatase activity is strong and restricted to the nuclear envelope of nuclei. 5'-Nucleotidase shows weak reaction deposit in whole nuclei but in contrast gives clear reaction deposit in isolated nuclear envelopes. Cytochemical reaction deposit due to nucleoside triphosphatase activity is not restricted to the nuclear envelope but is found to a larger extent within the nucleus.
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PMID:An enzymic analysis of a nuclear envelope fraction. 18 34

Membrane phosphorylation and nucleoside triphosphatase activity of sarcoplasmic reticulum vesicles isolated from rabbit skeletal muscle were studied using ATP and ITP as substrates. The Ca2+ concentration was varied over a range large enough to saturate either the high affinity Ca2+-binding site or both high and low affinity binding sites. In intact vesicles, which are able to accumulate Ca2+, the steady state level of enzyme phosphorylated by either ATP or ITP is already high in 0.02 mM Ca2+ and does not vary as the Ca2+ concentration is increased to 10 mM. Essentially the same pattern of membrane phosphorylation by ATP is observed when leaky vesicles, which are unable to accumulate Ca2+, are used. However, for leaky vesicles, when ITP is used as substrate, the phosphoenzyme level increases 3- to 4-fold when the Ca2+ concentration is raised from 0.02 to 20 mM. When Mg2+ is omitted from the assay medum, the degree of membrane phosphorylation by ATP varies with Ca2+ in the same way as when ITP is used in the presence of Mg2+. Membrane phosphorylation of leaky vesicles by either ATP or ITP is observed in the absence of added Mg2+. When these vesicles are incubated in media containing ITP and 0.1 mM Ca2+, addition of Mg2+ up to 10 mM simultaneously decreases the steady state level of phosphoenzyme and increases the rate of ITP hydrolysis. When ATP is used, the addition of 10 mM Mg2+ increases both the steady state level of phosphoenzyme and the rate of ATP hydrolysis. When the Ca2+ concentration is raised to 10 or 20 mM, the degree of membrane phosphorylation by either ATP or ITP is maximal even in the absence of added Mg2+ and does not vary with the addition of 10 mM Mg2+. In these conditions the ATPase and ITPase activities are activated by Mg2+, although not to the level observed in 0.1 mM Ca2+. An excess of Mg2+ inhibits both the rate of hydrolysis and membrane phosphorylation by either ATP or ITP.
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PMID:Calcium and magnesium regulation of phosphorylation by ATP and ITP in sarcoplasmic reticulum vesicles. 18 11

Spiroplasma citri was cultured in three different media that supplied cholesterol and fatty acids from: (i) horse serum, (ii) pleuropneumonia-like organism (PPLO) serum fraction, or (iii) bovine serum albumin-fatty acid-cholesterol. The ability of PPLO serum fraction to support growth varied by lot number. Neither PPLO serum fraction nor the bovine serum albumin medium supported growth as well as the horse serum medium. Analysis of cholesterol, lipid phosphorus, and membrane protein showed the horse serum- and PPLO-grown cells to be indistinguishable, but the bovine serum albumin-grown cells were deficient in lipid phosphorus. The three cultures did not show markedly different fatty acid compositions, but, in all cases, the cultures preferentially incorporated palmitic acid and discriminated against linoleic acid. Cultures grown for different times from logarithmic growth through a degenerative phase showed relatively constant ratios of cholesterol/protein and lipid phosphorus/protein. Fatty acid composition was also relatively constant at the different stages. Adenosine triphosphatase and p-nitrophenyl phosphatase were mainly associated with the membrane, whereas reduced nicotinamide adenine dinucleotide oxidase was either readily removed or not associated with the membrane. The reduced nicotinamide adenine dinucleotide oxidase was inactivated at temperatures above 35 degrees C.
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PMID:Composition and enzyme activities of Spiroplasma citri membranes. 19 32

Electron histochemical studies show that changes in the nucleoside triphosphatase activity in plasma membranes of cancer cells can proceed in different directions. Some cells show a high activity of magnesium-dependent NTPase over the whole membrane surface (perimeter), while others have a low enzymic activity which is present only in certain regions of the membranes, the remaining cells possessing no enzyme activity at all. These changes are not strictly characteristic of cancer cells alone.
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PMID:Hydrolysis of nucleoside triphosphate in plasma membranes of the hepatocytes of normal, regenerating and foetal livers and in cancer cells of hepatomas. 19 42


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