Effect of ethanol on ATP-hydrolase activity of myometrial actomyosin

In order of estimating some regularities of ethanol effective action on the uterus smooth muscles contractile proteins the effects of spiritus introduced into incubation medium on myometrium actomyosine ATP-hydrolase activity and superprecipitation was studied. ATP-hydrolase activity was displayed as more sensitive to ethanol action; its dependence on ethyl spiritus concentration had three-phase character expressed in two inhibiting and one activating sites. While defining the kinetic parameters of ATP hydrolysis reaction catalysed by uterus myometrium the correlation between inhibition the ATP-hydrolase activity of myometrium contractile complex under introducing into incubation medium 2% ethanol and decreasing the affinity of actomyosine to Mg2+ was made; the highest activating effect of ethanol on ATP-hydrolase activity of actomyosine complex in the presence of 8% ethanol correlated with increasing the affinity of actomyosine to Mg2+ and ATP.     

Effect of eosin Y on ATPase activity of actomyosine complex of the uterus smooth muscle

The effect of eosin Y (2,4,5,7 - tetrabromofluorescein; 0.1-100 microM) on ATPase activity smooth muscle actomyosine was studied. The inhibition coefficient i50 of ATPase activity with eosin Y was 0.74 +/- 0.07 microM. The inhibitor decreased V(max) of actomyosine ATPase for ATP, but no influence on affinity of actomyosine for ATP was observed. It is suggested that eosin Y inhibits actomyosine ATPase activity noncompetitively in respect of ATP.     

Several classes of binding sites for metals and nucleotides on yeast mitochondrial oligomycin sensitive ATPase.

The binding properties of Mg2+, Mn2+ and Co2+ to yeast mitochondrial oligomycin sensitive ATPase complex are studied, as reflected by their catalytic effect (hydrolysis of ATP or pNPP, a pseudo substrate) or by a physical parameter (atomic absorption, electron paramagnetic reasonance of Mn2+, enhanced fluorescence of chelating chlorotetracyclin). At least two classes of sites with very different affinities respectively around 10(-5) M and 10(-4) M are demonstrated: high affinity sites for cations which participate in pNPP hydrolysis and can bind ADP or ATP, although they have a poor efficiency for ATP hydrolysis, and low affinity sites for cations which participate efficiently in both pNPP and ATP hydrolysis. The possibility that the tight site class has itself two sub-classes is also discussed.     

Effect of spermine on activity of purified Ca2+, Mg2+-ATPase from plasma membranes of myometrium cells

Effect of endogenous polyamine spermine, a relaxant of smooth muscle, on the activity of myometrium cell plasma membrane Ca2+, Mg(2+)-ATPase was studied. It was observed a tendency to activation of enzyme at the spermine concentrations 0.1-0.5 mM, the increase of the polyamine concentrations up to 10 mM inhibited. ATPase by 80% (I50 = 5.5 +/- 0.3 mM). Spermine inhibited enzyme decreasing its turnover rate and affinity for Ca2+. The ATPase affinity for Mg2+ increased in the presence of spermine. It was revealed, that the inhibitory effect of spermine is changed by the stimulatory effect under the increase of Ca2+ concentration (up to 2.6 microM), that correlates with the relaxing effect of this polyamine on the smooth muscle.     

IMIPRAMINE-INDUCED CHANGES OF BRAIN ADENOSINE TRIPHOSPHATASE ACTIVITY

Abstract— Adenosine triphosphatase (ATPase) activities of brain microsomal and synaptosomal preparations are inhibited by imipramine [5-(3'-dimethylamino propyl)-10, 11-dihy-dro-5H-dibenz (b,f) azepine] in vitro , whereas microsomal ATPase activity is stimulated and synaptosomal ATPase activity remains unaltered under in vivo imipramine treatment. The inhibition of ATPase activity can to some extent be counteracted by spermine [N, N'-bis(3 aminopropyl)-1,4-butanediamine]. Determination of K_m values from double reciprocal plots (activity^-1 vs. ATP mM^-1) under drug and spermine-treated conditions appear to indicate that spermine can to some extent imparta stabilizing effect mainly on the microsomal membrane ATPase, preventing inhibition in presence of imipramine in vitro , although spermine has no effect on the already destabilized membrane ATPase. Spermine exerts a stabilizing effect on membrane ATPase possibly by increasing the affinity of the enzyme for the substrate.     

Nickel(II) transport in human blood serum. Studies of nickel(II) binding to human albumin and to native-sequence peptide, and ternary-complex formation with l-histidine

1. The initial rapid phase of ATP hydrolysis by bovine heart submitochondrial particles or by soluble F1-ATPase is insensitive to anion activation (sulphite) or inhibition (azide). 2. The second slow phase of ATP hydrolysis is hyperbolically inhibited by azide (Ki approximately 10(-5) M); the inosine triphosphatase activity of submitochondrial particles or F1-ATPase is insensitive to azide or sulphite. 3. The rate of interconversion between rapid azide-insensitive and slow azide-sensitive phases of ATP hydrolysis does not depend on azide concentration, but strongly depends on ATP concentration. 4. Sulphite prevents the interconversion of the rapid initial phase of the reaction into the slower second phase, and also prevents and slowly reverses the inhibition by azide. 5. The presence of sulphite in the mixture when ADP reacts with ATPase of submitochondrial particles changes the pattern of the following activation process. 6. Azide blocks the activation of ATP-inhibited ATPase of submitochondrial particles by phosphoenolpyruvate and pyruvate kinase. 7. The results obtained suggest that the inhibiting effect of azide on mitochondrial ATPase is due to stabilization of inactive E*.ADP complex formed during ATP hydrolysis; the activation of ATPase by sulphite is also realized through the equilibrium between intermediate active E.ADP complex and inactive E*.ADP complex.     

Oxygen exchange between phosphate and water accompanies calcium-regulated ATPase activity of skinned fibers from rabbit skeletal muscle

The extent of oxygen exchange between phosphate and water has been measured for the calcium-regulated magnesium-dependent ATPase activity of chemically skinned fibers from rabbit skeletal muscle. The oxygen exchange was determined for isometrically held fibers by measuring with a mass spectrometer the distribution of 18O atoms in the product inorganic phosphate when ATP hydrolysis was carried out in H2(18)O. The extent of exchange was much greater in relaxed muscle (free Ca2+ less than 10(-8) M) than in calcium-activated muscle (free Ca2+ approximately equal to 3 X 10(-5) M). Activated fibers had an ATPase activity at least 30-fold greater than the relaxed fibers. These results correlate well with the extents of oxygen exchange accompanying magnesium-dependent myosin and unregulated actomyosin ATPase activities, respectively. In relaxed fibers, comparison of the amount of exchange with the ATPase activity suggests that the rate constant for the reformation of myosin-bound ATP from the myosin products complex is about 10 s-1 at 20 degrees C and pH 7.1. In each experiment the distribution of 18O in the Pi formed was incompatible with a single pathway for ATP hydrolysis. In the case of the calcium-activated fibers, the multiple pathways for ATP hydrolysis appeared to be an intrinsic property of the actomyosin ATPase in the fiber. These results indicate that in muscle fibers, as in isolated actomyosin, cleavage of protein-bound ATP is readily reversible and that association of the myosin products complex with actin promotes Pi release.     

Substrate specificity of soluble mitochondrial ATPase]

The parameters of the hydrolysis of ATP and several analogs by soluble mitochondrial ATPase were determined. Vmax of the reaction decreases within the range: 2'-desoxy-ATP greater than ATP greater than etheno-ATP greater than GTP greater than 3'-O-methylATP greater than UTP. ATP, 2'-desoxypATP, 3'O-methyl-ATP, GTP, and etheno-ATP are hydrolysed by soluble mitochondrial ATPase with close Km(app) values. CTP is not hydrolysed by the enzyme and does not inhibit the ATPase reaction at a concentration of 10(-2) M. Nucleoside triphosphate derivatives with an "open" ribose cycle 9-[1',5'-dihydroxy-4-(S)-hydroxymethyl-3'-oxapent-2' (R)-yl]adenyl-5'-triphosphate, and 1-[1',5'-dihydroxy-4'-(S)-hydroxymethyl-3'-oxapent-2'(R)-yl[cytosine-5'-triphosphate are effective inhibitors of ATPase (Ki approximately 5.10(-5)M). Mitochondrial ATPase binds the ATP analogs that have hydrocarbon radicals-(CH2)2-, -(CH2)3-, and (CH2)4- instead of the ribose residues: 9-(2'hydroxyethyl)adenyl-2'-triphosphate, 9-(3'-hydroxypropyl)-adenine-3'-triphosphate, and 9-(4'-hydroxybutyl)adenine-4'-triphosphyl)adenine-4'-triphosphate were not hydrolysed by the enzyme, although they inbibit the ATPase reaction (Ki 2.10(-4)M). 9-(2'-hydroxyethyl)adenine-2'-triphosphate is hydrolysed by ATPase eight times more slowly than ATP. It is suggested that the hydrolysis of the substrates of mitochondrial ATPase is- preceded by the binding of the substrates in a tense conformation in the active site of the enzyme.     

(Na, K)ATPase activity in membrane preparations of ouabain-resistant HeLa cells.

Membrane preparations from two independent ouabain-resistant HeLa cell clones, HI-B1 and HI-C1, each appear to contain two species of (Na,K)ATPase. Two-thirds of the total (Na,K)ATPase in each mutant is indistinguishable from the enzyme in preparations of wild type cells with respect to ouabain binding, ouabain inhibition of (Na,K)ATPase activity, and dependence of ATP hydrolysis on Na, Mg, K, and ATP concentration. The remaining (Na,K)ATPase activity in the mutants is up to 1000 and 10 000 times, respectively, more resistant to ouabain than wild type enzyme. Resistance results from a lower affinity of the mutant enzymes for the inhibitor. The presence of Na, K, or Mg has little or no effect on the degree of resistance expressed by the mutant enzymes, although the resistance of the wild type enzyme varies 400-fold in the presence of different ligands. Incubation with 5 X 10(-8) M ouabain abolishes the activity of the wild type enzyme without affecting the activity of the resistant enzymes. Using this procedure we compared the parameters of ATP hydrolysis via the resistant and wild type enzymes. Ouabain-resistant (Na,K)ATPase of HI-C1 has an apparent K0.5 for potassium 3-4 times higher than that of either wild type enzyme or the resistant enzyme of HI-B1.     

Affinity chromatography of H+-translocating adenosine triphosphatase isolated by chloroform extraction of Rhodospirillum rubrum chromatophores. Modification of binding affinity by divalent cations and activating anions.

1. ATPase isolated from Rhodospirillum rubrum by chloroform extraction and purified by gel filtration or affinity chromatography shows three bands (alpha, beta and gamma) upon electrophoresis in sodium dodecyl sulphate. 2. Ca2+-ATPase activity of the preparation is inhibited by aurovertin and efrapeptin but not by oligomycin. Activity may be inhibited by treatment with 4-chloro-7-nitrobenzofurazan and subsequently restored by dithiothreitol. 3. The enzyme fails to reconstitute photophosphorylation in chromatophores depleted of ATPase by sonic irradiation. 4. Most of the active protein from the crude chloroform extract binds to an affinity chromatography column bearing an immobilised ADP analogue but not to a column bearing immobilised pyrophosphate. 5. In the absence of divalent cations, a component with a very high specific activity for Ca2+-ATPase is eluted from the column by 1.6 mM ATP. This protein migrates asa single band on 5% polyacrylamide gel electrophoresis and only possesses three subunits. At 12 mM ATP an inactive protein is eluted which does not run on acid or alkali polyacrylamide gels and shows a complex subunit structure. 6. ATPase preparations prepared by acetone extraction or by sonic irradiation of chromatophores may also be purified 10-fold by affinity chromatography. 7. The inclusion of 5 mM MgCl2 or CaCl2 during affinity chromatography of chloroform ATPase increases the capacity of the column for the enzyme and demands a higher eluting concentration of ATP. 8. When the enzyme is more than 90% inhibited by efrapeptin or 4-chloro-7-nitrobenzofurazan, the binding characteristics of the enzyme are not affected. 9. 10 mM Na2SO3, which greatly stimulates the Ca2+- and Mg2+-dependent ATPase activity of the enzyme and increases Ki (ADP) for Ca2+-ATPase from 50 to 850 micron, prevents binding to the affinity column. Binding may be restored by the addition of divalent cations. 10. Na2SO3 increases the rate of ATP hydrolysis, ATP-driven H+ translocation and ATP-driven transhydrogenase in chromatophores. 11. It is proposed that anions such as sulphite convert the chromatophore ATPase into a form which is a more efficient energy transducer.     

pH-dependence of kinetic parameters in the superprecipitation reaction and ATPase activity of myometrial actomyosin

The investigation of pH-dependence of superprecipitation reaction and ATPase activity of myometrium actomyosin in the interval of pH 5.5-8.0 has detected cupola-shaped curves with maximal activity of both processes by pH 6.5. On the basis of calculating the constants of ionization it was supposed that in the case of actomyosin ATPase imidazole groups of two histidins had an essential role in reaction of ATP hydrolysis and in superprecipitation process--imidazol group of histidine and carboxyl group of asparagin acid. The investigation of [ATP]- and [Mg2+]-dependence of superprecipitation reaction by pH 6.0, 6.5 and 7.0 has demonstrated different pH-sensitiveness of Michaelis constants and maximal speeds relatively Mg2+ and ATP for both processes. It was shown that pH-optimum of ATPase activity of myometrium actomyosin coincided with maximal affinity of actomyosin with ATP and Mg2+ while as for superprecipitation reaction the correlation between value of process by certain pH and affinity with ATP and Mg2+ was not detected.     

Several classes of binding sites for metals and nucleotides on yeast mitochondrial oligomycin sensitive ATPase

The binding properties of Mg²⁺, Mn²⁺ to yeast mitochondrial oligomycin sensitive ATPase complex are studied, as reflected by their catalytic effect (hydrolysis of ATP or pNPP, a pseudo substrate) or by a physical parameter (atomic absorption, electron paramagnetic resonance of Mn²⁺, enhanced fluorescence of chelating chlorotetracyclin). At least two classes of sites with very different affinities respectively around 10⁻⁵ M and 10⁻⁴ M are demonstrated : high affinity sites for cations which participate in pNPP hydrolysis and can bind ADP or ATP, although they have a poor efficiency for ATP hydrolysis, and low affinity sites for cations which participate efficiently in both pNPP and ATP hydrolysis. The possibility that the tight site class has itself two sub-classes is also discussed.     

Binding of intrinsic ATPase inhibitor to mitochondrial ATPase--stoichiometry of binding of nucleotides, inhibitor, and enzyme

F1-ATPase inhibitor was purified from yeast, Saccharomyces cerevisiae. The purified inhibitor blocked ATPase activity in the presence of ATP and Mg2+ by forming a latent equimolar enzyme-inhibitor complex with ATP and ADP newly bound to loose sites on the enzyme. A small portion of externally added ATP was hydrolyzed before the latent complex was formed but the hydrolysis was not directly related to the complex formation. Newly bound ATP tended to be converted to ADP when the ATP concentration of the medium was low. ATP tightly bound to the enzyme was not directly involved in formation of the complex. The complex was fairly stable in the presence of excess inhibitor and ATP but at a high concentration of the enzyme (10(-5) M), the inhibition was not complete, although only about 0.03% of the original activity remained unblocked.     

Dephosphorylation and reactivation of phosphorylated purified ox-kidney branched-chain dehydrogenase complex by co-purified phosphatase

The branched-chain 2 oxoacid dehydrogenase complex has been purified from well-washed ox-kidney mitochondria together with branched-chain dehydrogenase kinase. The complex was inactivated and phosphorylated by ATP in about 5 min at 30 degrees C. After hydrolysis of ATP by a contaminating ATPase (5-10 min) the complex was dephosphorylated and reactivated. Dephosphorylation and reactivation were linearly correlated. Reactivation was dependent upon Mg2+ (K0.5 greater than 1 mM) and inhibited completely by 50 mM fluoride. Reactivation and dephosphorylation are attributed to a mitochondrial branched-chain dehydrogenase phosphatase.     

Determination of the roles of active sites in F1-ATPase by controlled affinity labeling

The affinity reagents 3'-O-(5-fluoro-2,4-dinitrophenyl) [alpha-32P]ATP (FDNP-[alpha-32P]ATP) and 3'-O-(5-fluoro-2,4-dinitrophenyl) [8-14C]ATP (FDNP-[14C]ATP) were synthesized and used to characterize the structure and function of the three active sites in F1-ATPase. FDNP-[alpha-32P]ATP was found to bind covalently to F1 up to two DNP-[alpha-32P]ATP labels per F1 in the absence of Mg2+ without decreasing the ATPase activity. However, when MgCl2 was subsequently added to the reaction mixture, the enzyme could be further labeled with concomitant decrease in ATPase activity that is consistent with the complete inactivation of one enzyme molecule by an affinity label at the third ATP-binding site. Partial hydrolysis of the FDNP-[14C]ATP-labeled enzyme and sequencing of the isolated peptide indicated that the affinity label was attached to Lys-beta 301 at all three active sites. Samples of F1 with covalent affinity label on Lys-beta 301 were also used to reconstitute F1-deficient submitochondrial particles. The reconstituted particles were assayed for ATPase and oxidative phosphorylation activities. These results show that the catalytic hydrolysis of ATP either by F1 in solution or by F0F1 complex attached to inner mitochondrial membrane takes place essentially at only one active site, but is promoted by the binding of ATP at the other two active sites, and that ATP synthesis during oxidative phosphorylation takes place at all three active sites [corrected].     

Ca2+- or Mg2+-Dependent Enzymic ATP Hydrolysis Associated with the Microsomal Fraction of Frog Sciatic Nerves

The microsomal fraction of frog sciatic nerves was found to contain Ca2+- or Mg2+-dependent hydrolytic activity toward different nucleoside di- and triphosphates. In the presence of Ca2+ substrate specificity was in the order CTP > UTP > GTP > ATP. When Mg2+ was used, the triphosphates were approximately equally good substrates. ATP hydrolytic activity was very similar with Ca2+ or Mg2+ as the cofactor, whereas Ca2+ was the more potent activator of hydrolysis of the other triphosphates tested. The preparation showed some activity toward the nucleoside diphosphates but none toward the monophosphates or p-nitrophenylphosphate. The enzymic properties of ATP hydrolysis were more closely studied. The hydrolysis was optimal at 18--24 degrees C in the presence of 1 mM-Ca2+ or 1 mM-Mg2+. Ca2+- and Mg2+-ATP hydrolysis displayed pH maxima around 8.0--8.5 and 7.4--8.0, respectively. Vmax values for Ca2+- and Mg2+-ATP hydrolysis similar: approx. 12 mumol Pi per h per mg protein with a Km value of approx. 0.05 mM. The ATP hydrolysis activity was inhibited by NaF but unaffected by ouabain, vanadate, cytochalasin B, and various drugs known to influence ATPase activity of mitochondria. Zn2+ stimulated the ATP hydrolysis activity at low concentrations (10(-6)-10(-5) M) and inhibited it at higher concentrations. The possibility that these observations account for stimulation and inhibition of axonal transport in frog sciatic nerves exposed to similar concentrations of Zn2+ is discussed.     

ATP-dependent affinity change of Na+-binding sites of V-ATPase

V-type Na(+)-ATPase of Enterococcus hirae binds about six (6 +/- 1) Na(+) ions/enzyme molecule with a high affinity (Murata, T., Igarashi, K., Kakinuma, Y., and Yamato, I. (2000) J. Biol. Chem. 275, 13415-13419). After the addition of 5 mm ATP, the binding capacity dropped to about 2 (1.8 +/- 0.3) Na(+) ions/enzyme molecule, returning to the initial value concomitant with the decrease of ATP hydrolysis rate. These findings suggest that the affinity of four of six Na(+)-binding sites of the enzyme changes (lowers) in enzyme reaction. The ATP analogs (adenosine 5'-O-(3-thiotriphosphate) or 5'-adenylylimido-diphosphate), ADP, or aluminum fluoride that is postulated to trap ATPases at their transition state did not inhibit the Na(+) binding capacity significantly. Therefore, the affinity decrease of Na(+)-binding sites was unlikely to be due to ATP binding alone or at the transition state of ATP hydrolysis. In the presence of 5 mm ATP, the ATPase showed strong negative cooperativity (n(H) = 0.16 +/- 0.03) for Na(+) stimulation of ATPase activity. The Hill coefficient (n(H)) increased to 1 in parallel to the decrease of ATP concentration in the reaction mixture. Thus, the ATP-dependent affinity change cooperatively occurs in continuous enzyme reaction.     

Biochemical characterization of the plasma membrane Ca2+ pumping ATPase activity present in the gill cells of Mytilus galloprovincialis LAM

• 1.1. In the plasma membrane of mussel gill cells an ouabain insensitive, Ca²⁺-activated ATPase activity is present. The ATPase has high Ca²⁺ affinity (K_ma = 0.3 μM).
• 2.2. The optimum assay conditions to evaluate the enzymatic activity of the Ca²⁺-stimulated ATPase at 19°C are: 120–300 mM KCl ionic strength, pH 7.0 and 2 mM ATP. As for mammalian enzymes, the Ca²⁺ ATPase activity is stimulated by DTT (0.5–1 mM) and it is inhibited by low concentrations of vanadate (10–50 μM) and -SH inhibitors such as PCMB and PCMBS (10 μM); the enzyme appears to be calmodulin insensitive.
• 3.3. Electrophoretic analyses of plasma membrane proteins demonstrate that: (a) Ca²⁺ at n-μM concentrations is necessary to activate ATP hydrolysis with consequent formation of the enzyme-phosphate complex; (b) the steady state concentration of the phosphorylated intermediate is increased in the presence of La³⁺; (c) the mol. wt of Ca²⁺ ATPase is about 140 kDa.
• 4.4. Low Ca²⁺ concentrations (n-μM) are sufficient to stimulate the ATP-dependent Ca²⁺ uptake by plasma membrane inside-out vesicles.
• 5.5. The results indicate that the Ca²⁺ pump present in the gill plasma membranes could be responsible for Ca²⁺ extrusion and therefore involved in maintaining the cytosolic Ca²⁺ concentration within physiological levels.

     

The dnaB-dnaC replication protein complex of Escherichia coli. I. Formation and properties

The complex formed between the dnaB and dnaC replication proteins of Escherichia coli is stabilized by ATP binding to dnaC. The dnaB6-dnaC6-ATP6 complex can be maintained without ATP hydrolysis at a concentration as low as 5 x 10(-10) M. The complex is also formed with adenosine 5'-(gamma-thio)triphosphate but generates little or no dnaB activity, suggesting a requirement for ATP hydrolysis in the subsequent stage of binding of the complex to DNA. In this step, dnaC is released, leaving dnaB to function on the associated DNA.     

Mg, Ca-activated ATP-ase of Pacinian corpuscles]

Adenosine triphosphatase (ATPase) activated by Mg2+ or Ca2+ ions was detected in single mechanoreceptors (Pacini's corpuscles) of cat; addition of Ca2+ (10(-5)M) to Mg-ATP-ase increased the activity by the factor of 1.6. The activity optimum of Mg- or Co-ATPase was in the alkaline pH zone. A high substrate specificity of Mg, Ca-ATPase was shown. Parachlorinemercury-benzoate (5muM) considerably reduced the activity of Mg, Ca-ATPase, whereas oubain (10(-5)M) failed to affect it significantly. It is supposed that Mg, Ca-ATPase of Pacini's corpuscles was close to actomyosine -like proteins.