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PubMed1976

[Kinetics of Ca 2+ or Mg 2+ activated ATPase from lymphocyte plasma membranes].

The kinetic study of the C2+ ATPase activity of lymphocyte plasma memebranes allowed some properties of this enzyme to be evidenced. The Ca2+-activated hydrolysis of ATP is independent of a non-specific alkaline phosphatase. The substrate of the ATPase activity is the chelate Ca2+- ATP. Mg2+ may substitute for Ca2+ both as chelating ion and as activating ion. Several results suggest that we have only one ATPase, activated either by Ca2+-, or by Mg2+ with less efficiency; both chelates hve the same Km; pH values for maximum activity and transition temperatures are identical; the effects of free ions are also the same, activation at low concentration and inhibition at high concentration.

Adenosine Triphosphatases↗
PubMed1978

Reversible conversion from Ca(2)+-ATPase activity to Mg(2)+- and Mn(2)+-ATPase activities of coupling factor purified from acetone powder of Rhodospirillum rubrum chromatophores.

It is known that the coupling factor purified from the acetone powder of chromatophores from Rhodospirillum rubrum shows ATPase activity in the presence of Ca(2)+, but not in the presence of Mg(2)+ or Mn(2)+. The present study deals with conditions, under which the Ca(2)+-ATPase activity is reversibly converted into Mg(2)+- and Mn(2)+-ATPase activites with the purified coupling factor. 1. Of the pH indicators tested, 6 kinds coverted the Ca(2)+-ATPase activity into Mg(2)+- and Mn(2)+-ATPase activities in the order, ethyl orange greater than tropaeolin 000 greater than or equal to metanil yellow greater than tropaeolin 00 greater than ethyl red greater than or equal to bromthymol blue. 2. Of the detergents tested, those other than Triton X-100 and Brij 58 caused the conversion described above; dodecylsulfonate was most effective, whereas dodecylpyridinium chloride was moderately effective. 3. 2,4-Dinitrophenol stimulated approximately two-fold the Ca(2)+-ATPase activity, but not the Mg(2)+- or Mn(2)+-ATPase activity at all. However, in the presence of dodecylpyridinium chloride, the pH indicator remarkably stimulated the Mg(2)+- and Mn(2)+-ATPase activities, accompanied with a partial inhibition of the Ca(2)+-ATPase activity. Methyl red and ethyl red showed similar effects. 4. All the nucleoside triphosphates tested can serve as the substrate. ATP was most effective for the Ca(2)+-ATPase activity, whereas dATP was most effective for the Mg(2)+- and Mn(2)+-ATPase activities induced by ethyl orange. 5. In the presence of ethyl orange, the ATPase activity was induced by various divalent cations in the following order of effectiveness, Mg(2)+ greater than Zn(2)+ greater than CO(2)+ greater than Mn(2)+ greater than Ni(2)+. 6. The mechanism of the reversible conversion from the Ca(2)+-ATPase activity to the Mg(2)+- and Mn(2)+-ATPase activities by pH indicators and detergents is discussed.

Bacterial Chromatophores↗
PubMed1977

Acanthamoeba cofactor protein is a heavy chain kinase required for actin activation of the Mg2+-ATPase activity of Acanthamoeba myosin I.

We have purified a cofactor protein previously shown (Pollard, T. D., and Korn, E. D. (1973) J. Biol. Chem. 248, 4691-4697) to be required for actin activation of the Mg2+-ATPase activity of Acanthamoeba myosin I. The purified cofactor protein is a novel myosin kinase that phosphorylates the single heavy chain, but neither of the two light chains, of Acanthamoeba myosin I. Phosphorylation of Acanthamoeba myosin I by the purified cofactor protein requires ATP and Mg2+ but is Ca2+-independent. The Mg2+-ATPase activity of phosphorylated Acanthamoeba myosin I is highly activated by F-actin in the absence of cofactor protein. Actin-activated Mg2+-ATPase activity is lost when phosphorylated Acanthamoeba myosin I is dephosphorylated by platelet phosphatase. Phosphorylation and dephosphorylation have no effect on the (K+,EDTA)-ATPase and Ca2+-ATPase activities of Acanthamoeba myosin I. These results show that cofactor protein is an Acanthamoeba myosin I heavy chain kinase and that phosphorylation of the heavy chain of this myosin is required for actin activation of its Mg2+-ATPase activity.

Actins↗
PubMed1975

Sodium- and potassium-activated ATPase. A possible target of aldosterone.

Na-K-ATPase activity was measured with an ultramicromethod in single portions of the proximal and distal convolution and of the thick ascending limb of Henle from adrenalectomized rats and after treatment with 5 mug aldosterone per 100 g body wt. The activity in all tubular structures returned to normal within 1 h after injection. This rapid activation of Na-K-ATPase induced by hormone was completely prevented by actinomycin D and cycloheximide. It appears that this aldosterone effect on Na-K-ATPase requires an intact protein synthetic process.

Adenosine Triphosphatases↗
PubMed1977

Interactions of Tetrahymena dynein with microtubule protein. Tubulin-induced stimulation of dynein ATPase activity.

The ATPase (EC 3.6.1.3) activity of 30 S dynein from Tetrahymena cilia was remarkably stimulated by porcine brain tubulin at pH 10. The activity increased with increasing concentration of tubulin until the molar ratio of tubulin dimer to 30 S dynein reached approx. 10. The optimum of the ATPase activity of 30 S dynein in the presence of tubulin was 1-2 mM for MgCl2 and 2 mM for CaCl2. Increasing ionic strength gradually inhibited the stimulation effects of tubulin. Activation energies of 30 S dynein in the presence and absence of tubulin were almost the same. At the temperatures beyond 25 degrees C stimulation effects of tubulin disappeared. ATP was a specific substrate even in the presence of tubulin. In kinetic investigations parallel reciprocal plots were observed in a constant ratio of divalent cations to ATP of 2, indicating that tubulin was less tightly bound to 30 S dynein in the presence of ATP than the absence. The similar results were obtained at pH 8.2. 14 S dynein and the 12 S fragment which have poor ability to recombine with outer fibers were also activated with brain tubulin.

Adenosine Triphosphatases↗
PubMedDate not supplied

[ATPase activity in neuronal and glial enriched fractions of cerebral cortex in normal conditions and with hyperoxia].

The ATP-hydrolyzing activity was studied without addition of the exogenic cations and in the presence of Ca2+, Mg2+, Na+, K+ in myelin of rat brain cortex fractions enriched with neurons and glia. In the variant without addition of the exogenic cations the fraction enriched with neurons possesses the highest specific activity of ATPase and the myelin fraction possesses the lowest one. Addition of Ca2+, Mg2+, Na+, K+, triton X-100 activates ATPase in the nerve tissue cell fractions, ouabain inhibits the Mg2+, Na+, K+-ATPase activity. Action of oxygen under high pressure changes the percentage of transport ATPases distribution in neuropile and decreases the share of Na+, K+-ATPase sensitive to ouabain in myelin of the nerve tissue fractions enriched with neurons and glia.

Adenosine Triphosphatases↗
PubMed1976

Effect of biogenic amines and GABA on ATPase activities in mouse tissue.

ATPase activities were studied in brain, kidney and liver (13,000 X g pellet) fraction from the mouse. Dopamine and norepinephrine added in vitro showed a dose-dependent stimulation of Na+ and K+ activated and oligomycin sensitive Mg2+ ATPase activities in brain but not kidney and liver tissue fractions. GABA and serotonin had no effect on ATPase in brain, but inhibited oligomycin sensitive Mg2+ ATPase activities in kidney and liver. The relationship between the enhancement of ATPase activity by neurotransmitters in brain and the neuronal excitation is discussed.

Adenosine Triphosphatases↗
PubMed1979

Phosphorylation and its effects on ATPase activity of cardiac and skeletal myosins.

Myosin isolated under phosphorylation conditions, showed an additional band of phosphorylated light chain. In the case of cardiac myosin, LC2 is the phosphorylated light chain whereas in skeletal myosin, it is the 18,000 dalton component known as DTNB light chain. There are no differences in K+-EDTA and Ca2+ activated myosin ATPase of cardiac and skeletal of control and phosphorylated myosins. Our experiments showed that the rat heart and skeletal muscle myosins isolated under phosphorylating conditions exhibited high phosphate content which is associated with higher actin activated Mg2+ ATPase activity of myosin as compared to control. Control myosin phosphorylated using myosin light chain kinase and Ca2+ also showed high actin activated myosin ATPase activity. Beef heart myosin isolated in the presence of phosphate buffer, also exhibited a higher level of phosphate followed by an increase in actin activation as compared to myosin isolated in the absence of phosphate buffer. All these experimental data suggest that there is a direct relationship between actin activation and the amount of phosphate incorporated as a result of phosphorylation.

Actins↗
PubMedDate not supplied

Phospholipids and ATPase activity of wild-type and ATPase deficient and uncoupled mutants of E. coli.

The ATPase activities and the amounts of individual phospholipids in E. coli wild types B163 and ML-308-225 as well as in the mutants AN120, DL54 and etc-15 have been examined. The ATPase activities and the amount of cardiolipin are higher in the stationary phase than in the log phase, whereas the amounts of phosphatidylglycerol and phosphatidylserine are lower in the stationary phase. The decreased ATPase activity of the mutants is not due to an altered phospholipid composition.

Adenosine Triphosphatases↗
PubMed1975

Properties of (Na+ plus K+)-activated ATPase in rat liver plasma membranes enriched with bile canaliculi.

Liver plasma membranes enriched in bile canaliculi were isolated from rat liver by a modification of the technique of Song et al. (J. Cell Biol. (1969) 41, 124-132) in order to study the possible role of ATPase in bile secretion. Optimum conditions for assaying (Na+ plus K+)-activated ATPase in this membrane fraction were defined using male rats averaging 220 g in weight. (Na+ plus K+)-activated ATPase activity was documented by demonstrating specific cation requirements for Na+ and K+, while the divalent cation, Ca(2+), and the cardiac glycosides, ouabain and scillaren, were inhibitory. (Na+ plus K+)-activated ATPase activity averaged 10.07 plus or minus 2.80 mumol Pi/mg protein per h compared to 50.03 plus or minus 11.41 for Mg(2+)-activated ATPase and 58.66 plus or minus 10.07 for 5'-nucleotidase. Concentrations of ouabain and scillaren which previously inhibited canalicular bile secretion in the isolated perfused rat liver produced complete inhibition of (Na+ plus K+)-activated ATPase without any effect on Mg(2+)-activated ATPase. Both (Na+ plus K+)-activated ATPase and Mg(2+)-activated ATPase demonstrated temperature dependence but differed in temperature optima. Temperature induced changes in specific activity of (Na+ plus K+)-activated ATPase directly paralleled previously demonstrated temperature optima for bile secretion. These studies indicate that (Na+ plus K+)-activated ATPase is present in fractions of rat liver plasma membranes that are highly enriched in bile canaliculi and provide a model for further study of the effects of various physiological and chemical modifiers of bile secretion and cholestasis.

Adenosine Triphosphatases↗
PubMedDate not supplied

L-Thyroxine effects upon ATPase activities of several subcellular fractions of liver of the rat and the guinea pig.

The effect of thyroxine administration upon ATPase activity of several subcellular fractions of livers from rats and guinea pigs has been studied. To determine a patho-physiological dose of levo thyroxine [T4] for guinea pigs, a dose-response curve was examined of T4 effect upon oxidative phosphorylatin of guinea pig liver mitochondria. Maximum stimulation of mitochondrial respiration without uncoupling of oxidative phosphorylation was found with 15 microgram of T4 per 100 g body weight per day. This dose of T4 stimulated Mg++ activated ATPase of plasma membranes of guinea pigs and slightly stimulated Mg++ activated ATPase of guinea pig liver nuclear membranes. Rat liver nuclear membrane ATPase was not responsive to thyroxine at doses from 5 to 150 microgram per 100 g body weight. T4 significantly stimulated Ca++ or Mg++ ATPase of mitochondria and microsomes from both rat and guinea pig liver. Microsomes from both species were maximally activated by Mg++ and no significant additional stimulation with Ca++ was found. Mitochondrial ATPase from both species showed significantly greater Ca++ plus Mg++ ATPase activity than did Mg++ alone. Ca++ activated ATPase was approximately equal to dinitrophenol stimulated mitochondrial ATPase. Maximum activation of microsomal ATPase in both species was found with 1 mM calcium. We conclude that at physiological-intracellular concentrations of Ca++ and Mg++, thyroxine probably stimulates Mg++ activated microsomal ATPase and Ca++ activated mitochondrial ATPase. A potential role of Ca++ as a moderator of thyroxine stimulated activity in mitochondria and the relation of calcium to other metabolic reactions that are thyroxine sensitive is discussed.

Adenosine Triphosphatases↗
PubMed1975

Microsomal (Na- +K+)-activated ATPase from frog skin epithelium. Cation activations and some effects of inhibitors.

A method is described for the extraction of microsomal ouabain-sensitive (a- + K+)-activated ATPase from separated frog skin epithelium. The method yields a microsomal fraction containing (Na+ K+)-stimulated activity in the range of 30- 40 nmol - mg -1 - min -1 at 26 degrees C. This portion which is also ouabain sensitive, is about half of the total activity in media containing Mg2+, Na+ and K+. These preparations also contain Mg2+-dependent or Ca2+-dependent activities which are not additive and which are not significantly affected by ouabain, Na+, K+ or Li+. The activations of the ouabain-sensitive ATPase activity by Mg2+, Na+, and K+ are similar to those described in other tissues. It is found that Li+ does not substitute for Na+ as an activator but in high concentrations does produce partial activation in the presence of Na+ with no K+. These results are pertinent to the reported observations of ouabain-sensitive Li+ flux across frog skin. It is concluded that this flux is not apparently due to a direct activating effect of Li+ on the sodium pump.

Adenosine Triphosphatases↗