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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)

An electron-microscopic study of a choroid plexus papilloma from the lateral ventricle of a child revealed fine structural features typical of normal choroid plexus tissue. Utilizing the Ernst technique for demonstrating ouabain-sensitive, potassium-dependent phosphatase activity, Na-K-ATPase was localized along the basal and lateral plasmalemmas of the tumor epithelium but not along the ventricular surface (apical plasmalemma). This localization is similar to that found in normal choroid plexus epithelium of all species studied to date.
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PMID:Choroid plexus papilloma. II. Ultrastructure and ultracytochemical localization of Na-K-ATPase. 13 1

In vertebrate smooth muscle actomyosin and myofibrils a myosin light chain of molecular weight about 20,000 becomes phosphorylated at the same Ca2+ concentration as required to stimulate the actin-activated ATPase activity of myosin. Further, the degree of phosphorylation in the preparations as well as in various reconstituted actomyosins is proportional to their measured Ca2+ sensitivity. The phosphorylation process is very rapid and is essentially completed before the rise in ATPase activity. The enzyme responsible for the observed myosin phosphoylation is a specific myosin light chain kinase which is routinely co-purified with myosin. This kinase is normally present in actomyosin and its removal together with tropomyosin leads to a complete loss of the actin-activated ATPase activity. It is suggested that the Ca-dependent phosphorylation of the light chain via the light chain kinase represents the initial step in the activation of myosin that leads to contraction. Relaxation is probably effected by an as yet uncharacterised light chain phosphatase.
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PMID:Ca-linked phosphorylation of a light chain of vertebrate smooth-muscle myosin. 13 9

1. Two distinct patterns of tryptic modification of the catalytic functions of purified (Na+ + K+)-ATPase can be related to the two previously described patterns of enzyme inactivation and cleavage of the large chain seen with NaCl and KCl (Jorgensen, P.L. (1975) Biochim. Biophys. Acta 401, 399-415). 2. With NaCl, in phase A, the rapid inactivation of 50-55% of the (Na+ + K+)-ATPase activity is associated with loss of 85% of the K+-phosphatase activity and an increase in Na+-ADP-ATP exchange activity to 150% of control. ATP binding and phosphorylation are unchanged and the inactivation may result from cleavage of bonds within the large chain which are involved in dephosphorylation reactions. In phase B with NaCl, ATP binding and phosphorylation are lost slowly in parallel to inactivation of (Na+ + K+)-ATPase and cleavage of the large chain to a fragment with Mr=78 000. 3. With KCl, cleavage of the large chain to almost equal fragments abolish ATP binding and phosphorylation in parallel to the inactivation of (Na+ + K+)-ATPase. An additional split seems required for inactivation of the K+-pNPPase activity. 4. After completion of the digestion in phase A with NaCl a stable preparation can be isolated in which the activity of (Na+ + K+)-ATPase is 40%. ATP binding and phosphorylation are 90%, K+-phosphatase is 15%, and Na+-ADP-ATP exchange is 150% of control. We currently examine if these levels are related to changes in phosphorylation kinetics. 5. The ATP binding area is much more stable to trypsin with NaCl than with KCl, but loss of the binding capacity is in both cases correlated to a distinct cleavage of the large chain. The relationship between the fractional loss of ATP binding and cleavage of the large chain suggests that the nucleotide binding area is confined to one of the two large chains in the protein complex with Mr=270 000 which binds one molecule of ATP. 6. The data also suggest that the phosphatase site is remote from the ATP binding area. It is proposed that the protein complex with Mr=270 000 contains two large chains with different catalytic functions and that each chain forms a cation channel.
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PMID:Purification and characterization of (Na+ + K+)-ATPase. VI. Differential tryptic modification of catalytic functions of the purified enzyme in presence of NaCl and KCl. 13 23

Ultrastructural studies on the Malpighian tubules of Glomeris marginata (Villers) reveal considerable morphological differences between the upper, fluid secreting, segment, and the lower segment which is at present of unknown function. Previous reports have shown that the upper tubule has a high permeability to compounds of high molecular weight. This may be accounted for by the fact that the epithelium shows very extensive intercellular spaces which are linked directly to junctions apparently specialised to provide a low resistance extracellular pathway between the haemocoel and the tubule lumen. Histochemical studies on the localisation of phosphatase enzymes reveal intracellular vesicles with acid phosphatase activity. The basal labyrinth of the lower tubule exhibits considerable alkaline phosphatase activity which is apparently identical in location to the enzyme revealed by two different ATPase localisation techniques.
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PMID:Ultrastructural studies on the Malpighian tubule of the pill millipede, Glomeris marginata (villers). 14 32

Treatment of red cell membranes with pure phospholipase C inactivates (Na+ + K+)-ATPase activity and Na+-dependent phosphorylation but increases K+-dependent phosphatase activity. When phospholipase A2 replaces phospholipase C, all activities are lost. Activation of K+-dependent phosphatase by treatment with phospholipase C is caused by an increase in the maximum rate of hydrolysis of p-nitrophenylphosphate and in the maximum activating effect of K+, the apparent affinities for substrate and cofactors being little affected. After phospholipase C treatment K+-dependent phosphatase is no longer sensitive to ouabain but becomes more sensitive to N-ethylmaleimide. In treated membranes Na+ partially replaces K+ as an activator of the phosphatase. Although ATP still inhibits phosphatase activity, neither ATP, nor ATP+Na+ are able to modify the apparent affinity for K+ of K+-dependent phosphatase in these membranes.
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PMID:ATPase and phosphatase activities from human red cell membranes. III. Stimulation of K+-activated phosphatase by phospholipase C. 14 59

Phosphatase activity identified with Na+-K+-ATPase was localized at the basal surface of cerebral cortical capillary endothelium by perfusion with a p-nitrophenyl phosphate-strontium medium. The relationship of this to the blood-brain barrier to K+ is discussed.
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PMID:Cytochemical localization of the K+ regulation interface between blood and brain. 14 49

The influence of various bile acids on the (Na+-K+)-ATPase and Mg2+-ATPase activity of rat colon is described. At a concentration of 0.6 mmol/l C and TC did not inhibit the (Na+-K+)-ATPase activity in contrast to GC. The taurine derivates TC, TCDC and TDC did not influence or even enhanced the (Na+-K+)-ATPase activity. All bile acids except C, TC and CDC depressed the Mg2+-ATPase activity. At higher concentrations only C and TC did not influence the (Na+-K+)-ATPase activity. C, GC and TC at 2.5 mmol/l decreased the (Na+-K+)-activated phosphatase with ATP as substrate. All other substrates tested did not influence the enzymic activity significantly. The results indicate that bile acids can inhibit the Na+-absorbing system in rat colon. Hence this inhibition can cause diarrhea.
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PMID:Influence of bile acids on the (Na+-K+)-activated- and Mg2+-activated ATPase of rat colon. 14 61

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.
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PMID:Acanthamoeba cofactor protein is a heavy chain kinase required for actin activation of the Mg2+-ATPase activity of Acanthamoeba myosin I. 14 30

An extension of a previous model [2] is proposed of the glycolysis of erythrocytes which includes realistic rat laws for the hexokinase-phosphofructokinase system and for the 2,3-P2G phosphatase. Whereas most conclusions previously drawn are reinforced, the mechanism of ATP regulation is different in the present model. The ATP concentration is mainly regulated by the inhibitory action of ATP and the activating effect of AMP on the phosphofructokinase. The role of the 2,3-P2G bypass as a buffer of changes in the ATP demand is of lesser significance than previously thought. Besides the feedback action of the adenine nucleotides on the hexokinase-phosphofructokinase system in the quasisteady state the role of 2,3-P2G as an energy source is important since it can yield ATP for a certain period of time. The present version of the model describes qualitatively the experimental data on the modulation of Na+-K+-ATPase.
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PMID:An extended model of the glycolysis in erythrocytes. 14 74

Three proteins possessing alkaline phosphatase activity were detected in a fraction of periplasmic material of Escherichia coli K-10 and its mutants with constitutive synthesis of alkaline phosphatase. They also showed acid phosphatase, pyrophosphatase and ATPase activities. Through the use of phosphatase-negative mutants it was shown that these proteins were the products of a single structural gene and therefore represented alkaline phosphatase isozymes. The numbers of enzyme isoforms and possibly the spectrum of their phosphohydrolase activities were controlled by exogenous orthophosphate and depended on the integrity of regulator genes for alkaline phosphatase.
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PMID:Metabolic and genetic control of isoenzyme spectrum of alkaline phosphatase in Escherichia coli. 14 52


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