Ecto-ATPase

Somlyo Why do you need the apyrase Doesn t the human uterus have enough ecto-ATPase There is a lot of ecto-ATPase in most smooth muscles. Is it not high in human uterus ... 

In 1991 bile-acid secretion was shown to be energy driven by a 110-kDa glycoprotein that was dependent on ATP. This protein was subsequently characterised as liver ecto-ATPase by Sippel and co-workers. However, while further work with COS cells showed that expression of ecto-ATPase enhanced secretion of bile acids purified canalicular membranes lacking this enzyme efficiently exported bile acids showing that at least one other bile-acid transporter existed. ... 

Gleeson R. A., Trapido-Rosenthal H. G., McDowell L. M., Aldrich H. C. and Carr W. E. (1992) Ecto-ATPase/phosphatase activity in the olfactory sensilla of the spiny lobster, Panulirus argus localization and characterization. Cell Tissue Res. 269, 439-445. 

Experimental methods will not be described since these are detailed in the literature P2X purinoceptors [26-30] P2Y-purinoceptors [29-31] P2U purinoceptors [30] P2T-purinoceptors [32] ecto-ATPase assay [31]. 

Figure 6. Residual ecto-ATPase activity in guinea-pig taenia coli using ATP (0.1 mM) as substrate in the absence and presence of PPADS [31].

An ac field could also stimulate ATP hydrolysis activity of sheep kidney Na, K-ATPase and Ecto nucleotide diphosphohydrolase, at 37 °C (31). ATP hydrolysis does not require energy input. The increase in the ATP splitting activity reflects the sensitivity of chemical rate constants to an electric field as in eqs 7 and 8. Figure 3 shows the ATP hydrolysis activity of Ecto ATPase at 37 °C as a function of frequency when a 5.0-V/ cm (peak-to-peak) ac field was used. As mentioned, Blank and Soo used 1-mV/ cm ac fields to stimulate the ATP splitting activity of Na, K-ATPase (19, 20). Their results are also presented here. 

Nucleosidemonophosphates do not serve as substrates, Ecto-ATPase activity requires the presence of a divalent cation in most systems. For operational reasons, the application of the term Ca -ATPase or Mg -ATPase is satisfactory, because in many cells the enzyme is activated by various concentrations of either cation. 

We have found that the ecto-ATPase is optimally stimulated by Mn at concentrations of 3 x 10" or below, but we have also observed some exceptions (for instance, in mouse neuroblastoma where 10 M Ca was most effective and Mn did not stimulate). Mn concentrations in excess of 3 x 10 M are inhibitory. The ecto-ATPase seems widely distributed in eukaryotic cells. There has been an earlier report that the enzyme was not present on the surface of intact neurons (CUMMINS HYDEN, 1962) but it certainly is present on the surface of intact neuroblastoma cells (TRAMS 6e LAUTER, 1974 STEFANOVIC et ad, 1976b), Conventional sulfhydryl compounds or inhibitors have little effect on the enzyme and ouabain is not inhibitory. We have found that ecto-ATPase of cultured CNS cells was inhibited by certain phenothiazine derivatives. Micromolar concentrations of thiazines and tricyclic antidepressants were inhibitory in rat leukocytes (MEDZIHRADSKY et, 1975). There has been one report that adipocyte membrane Mg ATPase was markedly stimulated by insulin and by Concanavalin A (JARRETT Sc SMITH, 1974). ... 

A moderate increase in specific activity of ecto-ATPases with an increase in cell density per culture was recently reported in N-18, N-115 and NN cell lines (STEFANOVIC, 1976b). NN cell cultures... 

Ecto-ADPase. This enzyme was first described in chick embryo fibroblasts (PERDUE, 1970) and in human erythrocytes (PARKER, 1970). It apparently is distinct from the ecto-ATPase. We have observed the activity of an ecto-adenosinediphosphate phosphoesterhydrolase (EC 3.6.1.6) in various tissue culture monolayers but have not made an extensive study of the enzyme. Similarly to the ecto-ATPase, ecto-ADPase is stimulated by either Ca, Mg or Mn (PERDUE,... 

Zhang, X., Malhotra, R., and Guidotti, G. (2000). Regulation of yeast ecto-apyrase yndlp by activating subunit Vmal3p of the vacuolar H+-ATPase. J. Biol. Chem. 275, 35592-35599. 

Mihaylova-Todorova ST, Todorov LD, Westfall DP (2002) Enzyme kinetics and pharmacological characterization of nucleotidases released from the guinea pig isolated vas deferens during nerve stimulation evidence for a soluble ecto-nucleoside triphosphate diphosphohydrolase-like ATPase and a soluble ecto-5 nucleotidase-like AMPase. J Pharmacol Exp Ther 302 992-1001 Moos WH, Szotek DS, Bruns RF (1985) N6-Cycloal ky I adenosines. Potent Ai-selective adenosine agonists. J Med Chem 28 1383 4... 

Maxwell, W. L., McCreath, B. J., Graham, D. I., and Gennarelli, T. A., Cytochemical evidence for redistribution of membrane pump calcium-ATPase and ecto-Ca-ATPase activity, and calcium influx in myelinated nerve fibres of the optic nerve after stretch injury, J. Neurocytol., 24, 925, 1995. 

The strongest cases for ecto-enzymes as ubiquitous membrane constituents can be made for the 5 -nucleotidase and for a divalent cation-stimulated nucleoside polyphosphatase (Ca -ATPase). If these two enzymes are not obligatory on the external surface of all eukaryotic cells, then they certainly occur rather commonly as ecto-enzymes. Moreover, they probably occur in several forms, as iso-enzymes, and their properties appear to undergo changes with the physiological or developmental state of the cell (BLQMBERG RAFTELL, 1974 HEWLETT, 1976 ROSENBLATT, 1976). 

Ecto-nucleotide polyphosphatase. This enzyme was first observed in nucleated erythrocytes (WENKSTERN ENGELHARDT, 1957) generally, it is described as a Ca +-ATPase or Mg -ATPase (adenosinetriphosphate-5 -phosphoester hydrolase, EC 3.6.1.3). The enzyme has a high specificity for they -phosphate of nucleoside-triphosphates but a broad specificity for the riboside moiety. It is not quite clear if extracellular ADP is hydrolyzed by this enzyme, but the current evidence favors the existence of a separate ecto-ADPase. 

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