Nucleotidase, function

Zimmermann, H. 8r Braun, N. (1999). Ecto-nucleotidases - molecular structures, catalytic properties, and functional roles in the nervous system. Prog. Brain Res. 120, 371-85. 

Fig. 5. Illustration of the 5 -nucleotidase (TaqMan) assay for allele discrimination. (A) The allele discrimination assay employs two unlabeled PCR primers and two doubly fluorescent labeled PCR probes for visuaUzation of a mutant allele. The target sequence is initially denatured and amplified in the presence of each of the primers and probes. Increasing polymerization in the presence of a thermostable polymerase which contains a 5 proofreading function allows cleavage of one fluorescent indicator from an appropriate probe during the cycling reaction. (B) Probes are designed with a fluorescent reporter and a quencher moiety. AmpUfication reactions are spiked with additional fluorescent quenchers in order to render the reaction initially dark to the photomultipUer mbe or diode. The probes are designed...

Thus, there is likely as many as three enzymes with 5 -nucleotidase activity in liver, one lysosomal, one cytoplasmic, and one membrane bound. Their specificities and kinetic properties appear to be distinctly different. This would suggest specialized physiological functions not yet understood. 

Fig. 4 Mechanisms involved in the extracellular inactivation of nucleotides (a, b and c) and adenosine (d) and their influence on purine concentration in the P2Y and PI receptor biophases, (a) NT-PDasel hydrolyses ATP and ADP very efficiently, thus preventing their action on P2Y receptors (b) NTPDase2 metabolizes ATP preferentially, allowing an accumulation of ADP and thus favouring activation of P2Yi, 12,13 receptors (c) NTPDase3 hydrolyses both ATP and ADP slowly, giving them time to activate both P2Y2,4 and P2Y 1,12,13 receptors. Formation of adenosine depends on the activity of ecto 5 -nucleotidase (CD73). Adenosine inactivation systems also influence adenosine concentration in the PI receptor biophase (d) the nucleoside transporters take up adenosine adenosine deaminase (ADA) regulates both the concentration of adenosine in the Ai receptor biophase and the functionality of Ai receptors.

Zhang FL, Luo L, Gustafson E et al (2002) P2Y13 identification and characterization of a novel Gaj-coupled ADP receptor from human and mouse. J Pharmacol Exp Ther 301 705-13 Zhang JM, Wang HK, Ye CH et al (2003) ATP released by astrocytes mediates glutamatergic activity-dependent heterosynaptic suppression. Neuron 40 971-82 Zimmermann H (1992) 5 -Nucleotidase molecular structure and functional aspects. Biochem J 285 345-65... 

Alkaline phosphatase, acid phosphatase, 5 -nucleotidase, monoacyl hydrolase, ribonuclease, type 1 phosphodiesterase, adenosine triphosphatase, adenyl cyclase, glycosyl transferase, esterases and disaccharidase have been biochemically or cytochemically demonstrated in the tegument of various cestodes (152, 210, 250, 374, 491, 620, 624-626, 651, 718, 763, 776, 898). Several of these enzymes - phosphatases, 5 -nucleotidase and phosphodiesterase - probably have a digestive and/or absorptive function but the role of the others is uncertain. 

The reaction mixture contained cyclic formycin monophosphate, an analog of cAMP, as the substrate, Tris-HCl (pH 7.5) as buffer, and MgQ2. The reaction was started by the addition of the enzyme. Samples were removed at intervals and injected directly onto the reversed-phase column for analysis. Figure 9.108 shows chromatograms after 10 and 30 minutes of incubation. While the amount of cFoMP substrate in the incubation mixture has declined and the amount of product FoMP has increased, the amount of formycin A (FoA), the analog of adenosine, has remained unchanged. When the area of each peak is plotted as a function of reaction time, the data shown in the central inset are obtained. Although these data clearly illustrate the activity of the cyclic phosphodiesterase, they also show the absence of any 5 -nucleotidase. 

Lowenstein, JM, Yu, MK, Naito, Y, Regulation of adenosine metabolism by S -nucleotidase, In Regulatory functions of adenosine, (eds. Berne, RM., Rail, TW and Rubio, R), Martinus Nijhoff Publishers, The Hague, 1983, 117-131. 

Enzymes in this category include alanine and aspartate aminotransferases, glutamate dehydrogenase (GLD), ATP, 5 -nucleotidase (NTP), y-glutamyl transferase (GGT), glutathione S-transferase (GST), and serum cholinesterase (CHE). The aminotransferases and ALP are widely used. They have long been mistakenly called, as a group, liver function tests. They are not, of course, but the habit persists. GGT is widely available in the United States and on automated analyzers. The others have not been adopted as widely. 

Lipoxygenase Malate dehydrogenase Metallo-endopeptidase N-Methyl transferase Monoamine oxidase Mixed-function oxidase (cytochrome P450 dependent) NADH2 diaphorase NADPH2 diaphorase Neutral endopeptidase 24.11 Nitro oxide synthase Nitro reductase 5 -Nucleotidase Peroxidase... 

Nucleotidase (5 -N) is an integral glycoprotein of the cellular plasma membrane in a wide range of animal cells. Its functional role is still unclear. Possibilities. include recovery of purines and pyrimidines from the extracellular space, the extracellular formation of neuromodular adenosine from released nucleotidases and non-enzymatic functions related to the interaction of 5 -nucleotidase with compartments of the cytoskel-eton and extracellular matrix (Schoen et al., 1987). 5 -N catalyses the production of adenosine by the hydrolytic cleavage of 5 -nucleotide monophosphates (i.e. adenosine-5 -monophosphate). The development of 5 -N in the cerebellum was studied by Schoen et al. (1987, 1988, 1990). 

Generally, all conversions in the biosynthetic direction, i.e. iPARMP— iPAR— iPA (catalysed by 5 -nucleotidase, (EC 3.1.3.5), and adenosine nucleosidase, (EC 3.2.2.7), respectively, c/. Fig. 2) may also proceed in the opposite direction, i.e. base-— nucleoside — nucleotide (catalysed by adenosine phosphorylase and adenosine kinase, respectively). All these enzymes require both Ade and iPA or Ado and iPAR, respectively, as substrates. They were characterised in wheat germ [15-18] and lupin seeds [19]. Interestingly, no K, -constants were reported for Z-type cytokinins (see summary in [22]). However, as seen in H-labelled Z-derivatives feeding experiments, Z-type cytokinins are also interconverted in a similar way [82,121,122]. Moreover, the specificity of these enzymes is not too strict with respect to the side chain configuration and one may speculate that this complex may function for most if not all native cytokinins [21,81]. 

The present study was undertaken to study 3 selected purine pathway enzymes in infectious mononucleosis (IM). The enzymes concerned are adenosine deaminase (ADA), purine nucleoside phosphory-lase (PNP) and 5"-nucleotidase (5"-N). The enzymes were selected since the absence of these enzymes have been associated with clinically defective lymphoid function (1), and because abnormalities in the activities of ADA and PNP have been observed in leukemia (2,3)... 

Figure 7. Nuclease stability studies of the MPEG-conjugated anti-HIV 12mers in presence of a 1 1 mixture of diesterase and 5 -nucleotidase percent of intact oligonucleotides as function of time.

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