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PubMed1975

Acid phosphatase and adenosine triphosphatase activities in the cell wall of baker's yeast.

In order to establish whether a specific adenosine triphosphatase is present in yeast cell wall, hydrolysis rates for p-nitrophenylphosphate (acid phosphatase activity) and for ATP (ATPase activity) were compared under various conditions. Rate determinations were made with both, intact cells and with preparations containing secreted enzymes from protoplasts. Acid phosphatase and ATPase activities had the same pH profile and were susceptible in the same way to the repression by orthophosphate and to the inhibition by 2-deoxyglucose. The Lineweaver-Burk plot shows biphasic kinetic behaviour for the hydrolysis of either p-nitrophenylphosphate or ATP. This suggests the existence of two enzymes with different affinities for the substrates, or one enzyme with at least two active sites. The two activities differ in thermostability and only one activity could be completely abolished by heat treatment. The thermostable enzyme activity had K-m values of 0.475 mM for p-nitrophenylphosphate, and 0.040 mM for ATP. ATP behaved as a partially competitive inhibitor of p-nitrophenylphosphate hydrolysis. Substrate competition studies showed that only a non-specific acid phosphatase is responsible for the hydrolysis of ATP.

4-Nitrophenylphosphatase↗
PubMed1967

Sodium-potassium adenosine triphosphatase: acyl phosphate "intermediate" shown to be L-glutamyl-gamma-phosphate.

Peptides obtained from pepsin digestion of the phosphorylated and nonphosphorylated forms of a preparation of brain microsomal sodium-potassium-activated adenosine triphosphatase were treated at pH 5.4 with N-(n-propyl-2,3-(3)H) hydroxylamine of high specific activity, then separated by column chromatography, and further digested with pronase. A compound isolated in higher amounts from the phosphorylated enzyme than from the nonphosphorylated enzyme migrated with authentic L-glutamyl-gamma-propylhydroxamate in four chromatographic systems and on electrophoresis on paper at three different pH's. The acyl phosphate "intermediate" in the phosphorylated form of the adenosine-triphosphatase therefore appears to be an L-glutamyl-gamma-phosphate residue.

Adenosine Triphosphatases↗
PubMed1978

Thermal denaturation of Micrococcus lysodeikticus adenosine triphosphatase. Influence of temperature on the circular dichroism, fluroescence and enzymic activity of the protein.

The soluble ATPase (adenosine triphosphatase) from Micrococcus lysodeikticus underwent a major unfolding transition when solutions of the enzyme at pH 7.5 were heated. The midpoint occurred at 46 degrees C when monitored by changes in enzymic activity and intrinsic fluorescence, and at 49 degrees C when monitored by circular dichroism. The products of thermal denaturation retained much secondary structure, and no evidence of subunit dissociation was detected after cooling at 20 degrees C. The thermal transition was irreversible, and thiol groups were not involved in the irreversibility. The presence of ATP, adenylyl imidodiphosphate, CaCl2 or higher concentrations of ATPase conferred stability against thermal denaturation, but did not prevent the irreversibility one denaturation had taken place. In the presence of guanidinium chloride, thermal denaturation occurred at lower temperatures. The midpoints of the transition were 45 degrees C in 0.25 M-, 38 degrees C in 0.5 M-and 30 degrees C in 0.75 M-denaturant. In the highest concentration of guanidinium chloride a similar unfolding transition induced by cooling was observed. Its midpoint was 9 degrees C, and the temperature of maximum stability of the protein was 20 degrees C. The discontinuities occurring the the Arrhenius plots of the activity of this enzyme had no counterpart in variations in the far-u.v. circular dichroism or intrinsic fluorescence of the protein at the same temperature.

Adenosine Triphosphatases↗
PubMed1974

Inhibition of the soluble adenosine triphosphatase from mitochondria by adenylyl imidodiphosphate.

1. Adenylyl imidodiphosphate is an inhibitor with high affinity for the soluble ATPase (adenosine triphosphatase) from mitochondria. 2. The reaction of the inhibitor with the ATPase is slow and estimates for the association and dissociation reaction rate constants are given. 3. The number of binding sites for the inhibitor appears to be doubled in the presence of 2,4-dinitrophenol. 4. Adenylyl imidodiphosphate is less effective as an inhibitor of the ATPase activity of this enzyme than of the inosine triphosphatase activity. It is also less effective on the ATPase of frozen-thawed or intact mitochondria and did not inhibit ADP-stimulated respiration by intact mitochondria.

Adenosine Triphosphatases↗
PubMed1975

Active potassium transport coupled to active sodium transport in vesicles reconstituted from purified sodium and potassium ion-activated adenosine triphosphatase from the rectal gland of Squalus acanthias.

Vesicles containing a purified shark rectal gland (sodium + potassium)-activated adenosine triphosphatase-(NaK ATPase) were prepared by dialyzing for 2 days egg lecithin, cholate, and the NaK ATPase purified from the rectal gland of Squalus acanthias. These vesicles were capable of both Na+ and K+ transport. Studies of K+ transport were made by measuring the ATP-stimulated transport outward of 42K+ or 86Rb+. Vesicles were preloaded with isotope by equilibration at 4 degrees for 1 to 3 days. Transport of 42K+ or 86Rb+ was initiated by addition of MgATP to the vesicles. The ATP-dependent exit of either isotope was the same. Experiments are presented which show that this loss of isotope was not due to changes in ion binding but rather due to a loss in the amount of ion trapped in the vesicular volume. The transport of K+ was dependent on external Mg2+. CTP was almost as effective as ATP in stimulating K+ transport, while UTP was relatively ineffective. These effects of nucleotides parallel their effects on Na+ accumulation and their effectiveness as substrates for the enzyme. Potassium transport was inhibited by ouabain and required the presence of Na+. The following asymmetries were seen: (a) addition of external Mg2+ supported K+ transport; (b) ouabain inhibited K+ transport only if it was present inside the vesicles; (c) addition of external Na+ to the vesicles stimulated K+ transport. External Li+ was ineffective as a Na+ substitute. The specific requirement of external Na+ for K+ transport indicates that K+ exit is coupled to Na+ entry. Changes in the internal vesicular ion concentrations were studied with vesicles prepared in 20 mM NaCl and 50 mM KCl. After 1 hour of transport at 25 degrees, a typical Na+ concentration in the vesicles in the presence of ATP was 72 mM. A typical K+ concentration in the vesicles was 10 mM as measured with 42K+ or 6 mM as measured with 86Rb+. The following relationships have been calculated for Na+ transport, K+ transport and ATP hydrolysis: Na+/ATP = 1.42, K+/ATP =1.04, and Na+/K+ = 1.43. The ratio of 2.8 Na+ transported in to 2 K+ transported out is very close to the value reported for the red cell membrane. Potassium-potassium exchange similar to that observed in the red cell membrane and attributed to the Na+-K+ pump (stimulated by ATP and orthophosphate and inhibited by ouabain) was observed when vesicles were prepared in the absence of Na+. The results reported in this paper prove that the shark rectal gland NaK ATPase, which is 90 to 95% pure, is the isolated pump for the coupled transports of Na+ and K+.

Adenosine Triphosphatases↗
PubMed1985

Action of bepridil, a new calcium channel blocker on oxidative phosphorylation, oligomycin-sensitive adenosine triphosphatase activity, swelling, Ca++ uptake and Na+-induced Ca++ release processes of rabbit heart mitochondria in vitro.

Effects of bepridil [1-[3-isobutoxy-2]benzylphenyl-amino)propyl pyrrolidine) on oxidative phosphorylation, oligomycin-sensitive adenosine triphosphatase, swelling, Ca++ uptake and Na+-induced Ca++ release processes of mitochondria isolated from rabbit heart were investigated. Bepridil, in concentrations greater than 5 microM, produced uncoupling of oxidative phosphorylation and stimulated oligomycin-sensitive adenosine triphosphatase activity. At low concentrations it prevented inorganic phosphate-induced swelling and associated depression of oxidative phosphorylation. Its effectiveness in preventing swelling and depression of oxidative phosphorylation was found to be dependent on inorganic phosphate concentration. A concentration of 1 microM of bepridil was effective in producing 50% less depression of phosphorylating respiration in the presence of 10 mM inorganic phosphate. Concentrations of bepridil above 25 microM inhibited the rate of Ca++ uptake. A 50% inhibition of Ca++ uptake was observed at 93 microM bepridil. The rate of Na+-induced Ca++ release was also inhibited by bepridil. A 50% inhibition of the rate of Na+-induced Ca++ release occurred at 11 microM of bepridil. When the Na+-dependent Ca++ release process was about 80% inhibited by 25 microM bepridil, the uptake process still remained at the same level as the untreated control. Results suggest that in addition to reported effects on sarcolemma and sarcoplasmic reticulum, mitochondria are also affected by bepridil.

Adenosine Triphosphatases↗
PubMed1983

Cell-free synthesis of succinate dehydrogenase and mitochondrial adenosine triphosphatase of sweet potato.

Polyadenylated mRNA was isolated from aged slices of sweet potato root tissue and translated in a wheat germ cell-free system. The synthesis of apoprotein of the flavoprotein subunit of succinate dehydrogenase and two of the subunits of mitochondrial adenosine triphosphatase were detected by indirect immunoprecipitation. The molecular weights of the immunologically identified products were 3,000 and 8,000-9,000 daltons larger than the mature flavoprotein subunit of succinate dehydrogenase and the mature subunits of adenosine triphosphatase, respectively.

Adenosine Triphosphatases↗
PubMedDate not supplied

Inhibition of adenosine triphosphatase and carbonic anhydrase by contrast media.

In vitro inhibition of adenosine triphosphatase and carbonic anhydrase by several radiographic contrast media and other compounds was measured. The concentrations required for 50% inhibition were, in general, similar to those obtained for other enzymes. The effect of methylglucamine could not be determined for either enzyme because of interference with the assays.

Acetazolamide↗
PubMed1976

Calcium control of actin-activated myosin adenosine triphosphatase from Dictyostelium discoideum.

A protein fraction from the cellular slime mold Dictyostelium discoideum confers Ca2+-sensitivity on the activation of purified myosin adenosinetriphosphatase (ATP phosphohydrolase, EC 3.6.1.3) from Dictyostelium by purified Dictyostelium actin. That is, the fraction inhibits the actomyosin adenosine triphosphatase activity in the absence of Ca+ but not in the presence of Ca2+. This Ca2+-sensitizing factor affects only the actin-activated myosin adenosine triphosphatase and not the enzyme activity of myosin alone. The Ca2+-sensitivity is conserved when muscle actin replaces Dictyostelium actin, but is lost when muscle myosin replaces Dictyostelium myosin. The factor appears to be a protein since it is nondialyzable, is heat labile, and can be precipitated with ammonium sulfate. The factor can be purified 70-fold on an actin-affinity column.

Actins↗
PubMed1977

Membranous effects on adenosine triphosphatase activities of mitochondria from rat liver and Morris hepatoma 3924A.

Adenosine triphosphatase (ATPase) activities of sonically prepared submitochondrial particles of rat liver and Morris Hepatoma 3924A were compared as a function of changes in temperature. On Arrhenius plots, a discontinuity at 18 degrees was observed for the rat liver mitochondrial ATPase, while the hepatoma mitochondrial ATPase revealed a discontinuity at 20.4 degrees. Values for energy of activation of the rat liver and hepatoma mitochondrial ATPases were comparable below the break (34.5 and 35.5 kcal/mole, respectively) and above the break (11.6 and 9.2 kcal/mole, respectively). Solubilization of the mitochondrial membrances with Triton X-100 resulted in constant and similar values of energy of activation for the ATPases Km values of hepatoma and rat liver mitochondrial ATPases for adenosine triphosphate were similar in both the membrane-bound and solubilized states. The lack of uncoupler-stimulated ATPase activity in hepatoma mitochondria is apparently not due to membranous effects on the affinity of the ATPase for adenosine triphosphate.

Adenosine Triphosphatases↗
PubMed1977

Effect of di-2-ethylhexyl phthalate on the activity of succinic dehydrogenase and adenosine triphosphatase of some vital organs of rat.

Succinic dehydrogenase (SDH) and adenosine triphosphatase (ATPase) activity measured 21 days after 3 intraperitoneal injections of di-2-ethylhexyl phthalate (DEHP) was decreased in heart, lung and kidney while it remained unaltered in brain. Under in vitro conditions, only SDH was sensitive to DEHP, degree of inhibition being concentration-dependent. DEHP solubilized with Tween 80 inhibited the SDH activity significantly at small concentrations of 5 to 25 ppm. ATPase activity was not modified.

Adenosine Triphosphatases↗
PubMed1981

Photoaffinity labeling of mitochondrial adenosine triphosphatase by an azido derivative of the natural adenosine triphosphate inhibitor.

The natural mitochondrial ATPase inhibitor (IF1) was modified with a radioactivity labeled heterobifunctional and photosensitive reagent, methyl 4-azido(14C)benzimidate ((14C)MABI). Titration experiments of IF1 by (14C)MABI and tryptic maps of (14C)MABI-IF1 indicated that specific lysine residues in IF1 are preferentially labeled by (14C)MABI. Under appropriate conditions of labeling (1 to 2 lysine residues modified per IF1), MABI-IF1 exhibited the same inhibitory potency as native IF1 on the hydrolytic activity of the coupling factor 1 of mitochondrial ATPase (F1). The same conditions were required for inhibition of F1 by MABI-IF1 and IF1 (slightly acidic pH and presence of ATP and MgCl2). In photolabeling experiments, (14C)MABI-IF1 was used to investigate the localization of IF1 binding sites on F1. Upon photoirradiation, MABI-IF1 bound selectively to the beta subunit of soluble or membrane-bound F1. Adenylyl imidodiphosphate and quercetin, two compounds which partially mimic the inhibitory effect of IF1 on ATPase activity of F1, markedly prevented the binding of (14C)MABI-IF1 to F1; on the other hand, aurovertin, a specific ligand of the beta subunit of F1, did not affect the interaction between (14C)MABI-IF1 and F1. In the absence of light, (14C)MABI-IF1 was used as a reversible radiolabeled ligand with respect to membrane bound F1 to investigate F1-IF1 interactions to inside-out submitochondrial particles as a function of the energy state of the particles. Oxidation of NADH by submitochondrial particles resulted in a decrease of bound (14C)MABI-IF1; the effect was counteracted by antimycin. The data suggested that added (14C)MABI-IF1 is capable of exchanging with IF1 bound to F1 in submitochondrial particles and that the rate and extent of (14C)MABI-IF1 release are triggered by the proton-motive force developed by the particles.

Adenosine Triphosphatases↗
PubMed1975

The effects of substrate concentration on the Mg-adenosine triphosphatase activity of myosin.

Using myosin, heavy meromyosin, and subfragment-1 the steady state rate of Mg-modified adenosine triphosphatase (Mg-ATPase) was determined over a range of substrate concentrations between 10(-8) M and 5 X 10(-3)M, at 0.5 M and 0.05 M KC1 (pH 7.4 at 20 degrees C). At the substrate concentrations below 10(-5) M, myosin Mg-ATPase was observed to show that two active sites interact, as suggested by the analysis of transient kinetic studies (Walz, F. G., Jr.: J. Theor. Biol. 41, 357-373 (1973)). The increase in the activity at Mg-ATP concentrations higher than 10(-4) M corresponds to the binding of Mg-ATP to myosin sites not responsible for the catalytic action. With heavy meromyosin and subfragment-1, the activity was best expressed by the Michaelis equation. With heavy meromyonsin, the activation at high ATP concentrations is detectable, though not as pronounced as with myosin, but not with subfragment-1.

Adenosine Triphosphatases↗