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PubMed1990

Subcellular distribution of myocardial 5'-nucleotidase.

The controversial subject of the subcellular location of myocardial adenosine production was studied employing density gradient fractionation of heart muscle combined with a novel method for analyzing distribution profiles based on multiple regression (correlation) analysis. Bungarotoxin binding, N-acetyl-beta-D-glucosaminidase, cytochrome c oxidase, NADPH-dependent cytochrome c reductase and lactate dehydrogenase were used as markers for the plasma membrane, lysosomes, mitochondria, sarcoplasmic reticulum and cytosol, respectively. The normalized distribution frequencies (fraction of total) of 5'-nucleotidase in mitochondria, lysosomes, plasma membranes, sarcoplasmic reticulum and cytosol in the 50 x g supernatant of total homogenate of heart muscle were found to be 0, 0.25, 0.44, 0.08 and 0.23, respectively. To increase the resolution power of this approach with respect to mitochondria, a crude mitochondrial fraction was also studied, in which the normalized distribution of 5'-nucleotidase in the homogenate was 0, 0.16 and 0.84 in mitochondria, plasma membranes and lysosomes, respectively. This mainly lysosomal 5'-nucleotidase activity was 61% inhibited by the alpha,beta-methylene analog of ADP, indicating that although the latter has been considered specific to the plasma membrane enzyme, it also inhibits the lysosomal enzyme. The intercellular distribution of 5'-nucleotidase was not studied, but the lack of this enzyme in the mitochondria indicate that the adenosine production observed during mitochondrial AMP production, e.g. during acetate oxidation in intact heart muscle, must involve AMP transport out from the mitochondria.

5'-Nucleotidase↗
PubMed1992

Myocardial adenosine formation during hypoxia: effects of ecto-5'-nucleotidase inhibition.

Release of adenosine and AMP into epicardial fluid and coronary venous effluent of isovolumic guinea-pig hearts was examined during normoxic (95% O2) and hypoxic (30% O2) perfusion with and without the ecto-5'-nucleotidase inhibitor alpha,beta-methylene adenosine diphosphate (AOPCP)*. Normoxic epicardial and venous adenosine levels were 221 +/- 27 and 67 +/- 11 nM, respectively, in untreated hearts. During 15 min of hypoxia, epicardial and venous adenosine levels increased in a phasic manner, reaching maximal values of 498 +/- 32 and 441 +/- 43 nM, respectively, during the initial 5 min of hypoxia. Epicardial and venous adenosine levels then declined slightly during the subsequent 10 min to 332 +/- 33 and 224 +/- 34 nM, respectively. Infusion of 50 microM AOPCP significantly reduced venous adenosine levels during normoxia (less than 50% of control), but was without effect on normoxic epicardial adenosine. Epicardial and venous adenosine levels increased during hypoxia with AOPCP but the increases were lower than those for untreated hypoxic hearts. Epicardial and venous adenosine levels recovered to baseline levels following 30 min of reoxygenation in both groups. Epicardial and venous AMP levels were elevated by AOPCP treatment during normoxia and hypoxia. Coronary vascular resistance decreased during hypoxia but the decline in resistance was less in AOPCP treated hearts. It is concluded that whereas basal interstitial adenosine levels appear to be independent of ecto-5'-nucleotidase activity, the hypoxic increase in interstitial adenosine is partially derived from an AOPCP sensitive ecto-5'-nucleotidase. Venous adenosine appears to be significantly dependent on ecto-5'-nucleotidase activity during normoxia and hypoxia.(ABSTRACT TRUNCATED AT 250 WORDS)

5'-Nucleotidase↗
PubMed1995

Distribution of 5'-nucleotidase in the developing mouse retina.

The distribution of 5'-nucleotidase was investigated in the developing mouse retina and also in the retina of the adult mouse and rat using a monospecific antibody directed against 5'-nucleotidase isolated from bovine brain. Already at the stage of the formation of the eye cup strong immunofluorescence was found at the ventricular surface. Throughout development the enzyme remained associated with the outer surface of the retina that corresponds to the former inner surface of the eye vesicle. During embryonic development immunoreactivity was also associated with the proliferating cellular elements which at that stage cannot yet be attributed to a defined retinal cell type. In the adult stage the surface-located retinal immunoreactivity is assigned to Müller cells with strongest fluorescence at the apical and microvilli containing cell compartment. Also the cellular processes in the outer nuclear layer, the outer plexiform layer and to a minor extent the inner nuclear layer revealed immunoreactivity. 5'-Nucleotidase immunoreactivity was found at the ventricular surface also of the adult brain. There it was associated with the apical surface of ependymal cells. Our results suggest that 5'-nucleotidase is of general functional importance for the metabolism of nucleotides at the ventricular surface of the retina as well as the ventricles of the brain, a feature that is maintained throughout development. Müller cells thus share not only functional characteristics of astrocytes and oligodendrocytes, as previously revealed, but also of ependymal cells to which they are closely related.

5'-Nucleotidase↗
PubMed1991

Purification and partial characterization of the soluble low Km 5'-nucleotidase from human seminal plasma.

Soluble low Km 5'-nucleotidase from human seminal plasma has been purified to homogeneity by one affinity and two gel-filtration chromatographic steps. The pure enzyme had a specific activity of 2000 nmol min-1 mg-1. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of purified low Km 5'-nucleotidase revealed a single polypeptide band of 40 +/- 7 kDa and a tetrameric structure of 160 +/- 10 kDa has been proposed for the native enzyme. The kinetic properties of low Km 5'-nucleotidase have been determined and rather unique characteristics have been found for this soluble low Km 5'-nucleotidase: the substrate efficiency was slightly higher for IMP with an optimum pH at 7.5; the enzyme showed an absolute dependence on Mg2+ ions. Ca2+ could replace Mg2+ ions for activity while other divalent cations could not substitute for Mg2+; the enzymes were equally activated by ATP and ADP up to 0.1 mM concentrations. At higher concentrations up to 1 mM, ADP was still an activator while ATP caused a gradual decrease of activation to the native activity. This effect could not be related to the Mg-ATP = complexes since the enzymic preparation Mg(2+)-free still showed the same biphasic pattern of activation.

5'-Nucleotidase↗
PubMed1990

5'-Nucleotidase is involved in chick embryo myoblast spreading on laminin.

Previous studies have shown that 5'-nucleotidase, an ectoenzyme from chicken gizzard, interacts specifically with laminin and fibronectin, two glycoproteins of the extracellular matrix. Recently, we demonstrated that 5'-nucleotidase was involved in the spreading of chick embryo fibroblast on laminin. In the present communication, we report that a monoclonal antibody (CG37) raised-directed against 5'-nucleotidase inhibited the spreading of chick embryo myoblasts on laminin after their initial attachment to the substrate. Furthermore, monoclonal antibody CG37 specifically eluted 5'-nucleotidase from immobilized laminin and thus enabled its isolation from other myoblast laminin-binding proteins.

5'-Nucleotidase↗
PubMed2006

In vitro exposure of heavy metals on nucleotidase and cholinesterase activities from the digestive gland of Helix aspersa.

Zinc, copper and cadmium are important environmental contaminants and differences in purinergic and cholinergic systems of invertebrates have been described when compared to characteristics of these signaling systems in vertebrates. Here we evaluate the effect in vitro of these metals on the ATPase, 5'-nucleotidase and cholinesterase (ChE) activities in the digestive gland of Helix aspersa. Zinc (500 and 1000 microM) promoted a significant decrease in 5'-nucleotidase activity. However, it did not induce changes in ATP hydrolysis. Copper (25 and 50 microM), inhibited significantly ATPase activity, but did not alter 5'-nucleotidase when compared to control (no metal added). In relation to effects of cadmium, an inhibitory effect on ATP hydrolysis has been observed at concentrations of 100, 500 and 1000 microM and a similar decrease of AMP hydrolysis was observed at 500 and 1000 microM. However, there were no significant changes in ChE activity from homogenates of the digestive gland of H. aspersa for all metals tested. This study demonstrated that zinc, cadmium and copper affect ATPase and 5'-nucleotidase in digestive gland, but not ChE, suggesting that the purinergic system may be a target related to toxicity induced by these metals and a possible indicator of biological impact of exposure to these contaminants.

5'-Nucleotidase↗
PubMed2006

Exposure to Hg2+ and Pb2+ changes NTPDase and ecto-5'-nucleotidase activities in central nervous system of zebrafish (Danio rerio).

Neurotransmission can be affected by exposure to heavy metals, such as mercury and lead. ATP is a signaling molecule that can be metabolized by a group of enzymes called ecto-nucleotidases. Here we investigated the effects of mercury chloride (HgCl(2)) and lead acetate (Pb(CH(3)COO)(2)) on NTPDase (nucleoside triphosphate diphosphohydrolase) and ecto-5'-nucleotidase activities in zebrafish brain membranes. In vitro exposure to HgCl(2) decreased ATP and ADP hydrolysis in an uncompetitive mechanism and AMP hydrolysis in a non-competitive manner. Pb(CH(3)COO)(2) inhibited ATP hydrolysis in an uncompetitive manner, but not ADP and AMP hydrolysis. In vivo exposure of zebrafish to HgCl(2) or Pb(CH(3)COO)(2) (20mug/L, during 24, 96h and 30 days) caused differential effects on nucleotide hydrolysis. HgCl(2), during 96h, inhibited the hydrolysis of ATP, ADP and AMP. After 30 days of exposure to HgCl(2), ATP hydrolysis returned to the control levels, ADP hydrolysis was strongly increased and AMP hydrolysis remained inhibited. Exposure to Pb(CH(3)COO)(2) during 96h caused a significant decrease only on ATP hydrolysis. After 30 days, Pb(CH(3)COO)(2) promoted the inhibition of ATP, ADP and AMP hydrolysis. Semi-quantitative RT-PCR analysis showed no changes in the expression of NTPDase1 and 5'-nucleotidase, following 30 days of exposure to both metals. This study demonstrated that Hg(2+) and Pb(2+) affect the ecto-nucleotidase activities, an important enzymatic pathway for the control of purinergic signaling.

5'-Nucleotidase↗
PubMed1976

Distribution of glucose-6-phosphatase and 5-nucleotidase in the digestive system of two teleost fishes.

The distribution and histochemical localization of G6Pase and 5-nucleotidase in the different parts of the alimentary canal of two teleost fishes, Heteropneustes fossilis and Barbus sophore have been studied. The major sites of activity of the two enzymes are intestinal mucosa and liver. G6Pase is localized in the cytoplasm of the absorptive cells of the intestinal mucosa while 5-nucleotidase is present in the cytoplasm as well as nucleus and cell membrane. In the intestine, the anterior portion shows more stronger activity than in the middle and posterior portions. Mild activity is also noticed in the mucosa and gastric glands of the stomach. G6Pase activity is stronger than 5-nucleotidase activity in all the portions. Weak 5-nucleotidase activity is found in the submucosal connective tissue and the nuclei of the intestine. The goblet cells, muscularis abd serosa are negative in all the portions. G6Pase activity is stronger in the herbivorous fish Barbus sophore than in the omnivorous form Heteropneustes fossilis. In the liver, stronger activity of two enzymes is localized in the hepatocytes surrounding the sinusoids. Connective tissue and endothelial lining are negative.

Animals↗
PubMed1996

Development of 5'-nucleotidase staining in the olfactory bulbs of normal and naris-occluded rats.

The distribution of the adenosine-producing ecto-enzyme 5'-nucleotidase was investigated histochemically in the developing rat olfactory bulb. Rat pups underwent either unilateral surgical occlusion of the right external naris or sham surgery on postnatal day 1. At 10, 20, or 30 days postpartum, horizontal sections of the olfactory bulb were reacted histochemically to reveal the locus and intensity of 5'-nucleotidase activity. Relative staining levels were determined by optical densitometry in standardized bulb regions. A marked, age-related increase in staining density was observed. Reaction product was found primarily in neuropil areas. The P10 and P20 control animals did not exhibit right/left differences in bulb staining; however, some laterality was observed in P30 animals. Inter-glomerular and regional variations were observed throughout the developmental period, including (1) differences between neighboring glomeruli; (2) a gradient in the dorsal-ventral axis of the bulb; and (3) a higher staining density in the medial-caudal portion of the bulb. In subjects with occluded nares, asymmetries in right/left bulb 5'-nucleotidase staining patterns were detected throughout development. Bulbs ipsilateral to the blocked nares exhibited increased staining density, suggesting that the procedure enhanced enzymatic activity. Understanding these variations in 5'-nucleotidase staining may be important for a complete understanding of the mechanisms of olfactory bulb maturation and may give insight into the possible role of this enzyme in synaptic malleability during nervous system development and regeneration.

5'-Nucleotidase↗
PubMed1997

5'-nucleotidase enzyme cytochemistry as a tool for revealing activated glial cells and malleable synapses in CNS development and regeneration.

The demonstration of 5'-nucleotidase in neural tissue is achieved at both the light and electron microscopic levels by means of an enzyme cytochemical lead method, which is specific, sensitive and fast. By its activity this adenosine-producing ecto-enzyme (EC 3.1.3.5) outlines cellular surface membranes at the ultrastructural level. It is classically known as a marker of myelin and of astrocytes as well as (activated) microglial cells in the mature nervous system. In recent years, we discovered that 5'-nucleotidase is transiently active within synaptic clefts under conditions of development and regeneration. The enzyme is also seen at terminals in the mature retina and olfactory bulb, where spontaneous synaptic turnover occurs at adulthood. Thus, 5'-nucleotidase cytochemistry is useful in revealing sites of glial reactions and synaptic plasticity in CNS development and repair. It is assumed that the molecule affects terminal formation and cell motility due to dual functions in adenosine production and cell adhesion. Finally, at the light microscopic level, 5'-nucleotidase activity displays a dense neuropil staining which identifies topographic sub-units of certain parts of the nervous system, such as the striosomes of the basal ganglia, ocular dominance columns of the visual cortex and parasagittal bands of the cerebellum.

5'-Nucleotidase↗
PubMed1998

Nucleotide and nucleoside analogues as inhibitors of cytosolic 5'-nucleotidase I from heart.

Substrate and product specificity studies were used to develop inhibitors of the cytosolic 5'-nucleotidase I (c-N-I) from myocardium. As measured by Vmax/Km, c-N-I preferred pyrimidine 2'-deoxyribonucleotides as substrates with thymidine monophosphate (TMP) being the most efficient. In product inhibition studies, thymidine inhibited noncompetitively and inorganic phosphate inhibited competitively, consistent with an ordered release of nucleoside prior to phosphate. Mirroring nucleotide substrate specificities, pyrimidine nucleosides were more potent product inhibitors than purine nucleosides. Thus, pyrimidine nucleotide and nucleoside analogues were developed as inhibitors. Phosphonate analogues of TMP were synthesized by a novel method. The most potent was the 5'-phosphonate of 3'-deoxythymidine (ddT) (apparent Ki value of 63 nM). In addition, pyrimidine nucleoside analogues were inhibitors with 5-ethynyl-2',3'-dideoxyuridine being the most potent (apparent Ki value of 3.7 microM). The most potent nucleotide and nucleoside inhibitor were both greater than 1000-fold more potent inhibiting c-N-I than the cytosolic 5'-nucleotidase II. The nucleoside analogue was also greater than 1000-fold more potent against c-N-I than the membrane ecto-5'-nucleotidase (e-N). Because the phosphonate analogues measurably inhibited e-N (apparent Ki values of 6-12 microM), the selectivity of the phosphonates for c-N-I versus e-N was less (40-200-fold). Because of the high selectivity for c-N-I versus both of the other 5'-nucleotidases, the nucleoside inhibitors of c-N-I may be useful biochemical tools in discerning the role that c-N-I plays in generating adenosine within myocardium.

5'-Nucleotidase↗
PubMed2004

NTPDase and 5'-nucleotidase activities in synaptosomes of hippocampus and serum of rats subjected to homocysteine administration.

Patients with homocystinuria, an inborn error of metabolism, present neurological dysfunction and commonly experience frequent thromboembolic complications. The nucleoside triphosphate diphosphohydrolase (NTPDase) and 5'-nucleotidase enzymes regulate the nucleotide/nucleoside ratio in the central nervous system and in the circulation and are thought to be involved in these events. Thus, the current study investigated the effect of homocysteine administration on NTPDase and 5'-nucleotidase activities, in the synaptosomal fraction of rat hippocampus, and on nucleotidase activities in rat serum. Twenty-nine-day-old Wistar rats were divided in two groups: group I (control), animals received 0.9% saline; group II (homocysteine-treated), animals received one single subcutaneous injection of homocysteine (0.6 micromol/g). Rats were killed 1 h after the injection. NTPDase and 5'-nucleotidase activities from brain and serum were significantly increased in the homocysteine-treated group. Results show that, in hippocampus, ATP and ADP hydrolysis increased by 20.5% and 20%, respectively, and AMP hydrolysis increased by 48%, when compared to controls. In serum, ATP and ADP hydrolysis increased 136% and 107%, respectively, and AMP hydrolysis increased 95%, in comparison to controls. The current data strongly indicate that in vivo homocysteine administration alters the activities of the enzymes involved in nucleotide hydrolysis, both in the central nervous system and in the serum of adult rats.

5'-Nucleotidase↗
PubMed2002

Expression of 5'-nucleotidase and alkaline phosphatase in human aqueous drainage channels.

PURPOSE: Lymphatic vessels and blood vessels can be distinguished histochemically by their expression of 5'-nucleotidase and alkaline phosphatase. The aim of this study was to compare the expression of these enzymes in human aqueous drainage channels with that seen in lymphatics and blood vessels. METHODS: Histological sections from the angular regions of human eyes were prepared both by enzyme histochemical and immunohistochemical methods to analyse 5'-nucleotidase and alkaline phosphatase expression. In some of these eyes, Indian ink-stained gelatin was injected into Schlemm's canal and the suprachoroidal space to facilitate the identification of aqueous drainage routes. RESULTS: There was no expression of 5'-nucleotidase in the endothelium of aqueous drainage channels. Ocular blood vessels were characterized by strong expression of alkaline phosphatase, whereas the cellular lining of Schlemm's canal, the collector channels, the aqueous veins and a scleral channel from the suprachoroidal space showed significantly weaker expression or no expression at all. CONCLUSION: The study failed to show a histochemical similarity between lymphatics and human aqueous drainage channels, as no expression of 5'-nucleotidase could be found in any part of the aqueous outflow pathway. The endothelium of aqueous drainage channels also differed from normal blood vessels by a much weaker expression of alkaline phosphatase. This makes a histochemical distinction between aqueous veins and scleral veins possible.

5'-Nucleotidase↗
PubMed1973

Properties of a 5'-nucleotidase purified from mouse liver plasma membranes.

1. Extraction of a mouse liver plasma-membrane fraction with a detergent buffer, N-dodecylsarcosinate-Tris buffer (sarcosyl-Tris buffer), solubilized 90% of the protein and 70% of the 5'-nucleotidase activity. 2. The proteins of the sarcosyl-Tris buffer extract were fractionated by a rate-zonal centrifugation in a sucrose-detergent gradient. The major protein peak sedimented ahead of phospholipids, which mainly remained in the overlay. Glycoproteins were separated ahead of the protein peak. 3. The 5'-nucleotidase activity peak was associated with 5% of the protein applied to the gradient, and contained relatively few protein bands. 4. The 5'-nucleotidase was purified further by gel filtration on Sepharose and Sephadex columns equilibrated with sarcosyl-Tris buffer, to give a single glycoprotein band on sodium dodecyl sulphate-polyacrylamide-gel electrophoresis. The purified enzyme was lipid-free. 5. Electrophoresis in polyacrylamide gels in sarcosyl-Tris buffers showed that the enzymic activity was coincident with the protein band. 6. The molecular weight suggested for the enzyme activity by gel filtration or centrifugation in sucrose gradients was 140000-150000. Sometimes, a minor enzyme peak of lower molecular weight was obtained. 7. Polyacrylamide-gel electrophoresis in sodium dodecyl sulphate indicated that as the polyacrylamide concentration was increased from 5 to 15%, the apparent molecular weight of the enzyme decreased from 130000 to 90000. 8. The evidence that 5'-nucleotidase is composed of two active and similar, if not identical, glycoprotein subunits and the role of detergent in effecting the separation of membrane proteins and glycoproteins are discussed. 9. Substrate requirements, pH optima and the nature of inhibition by an analogue of adenosine diphosphate are reported.

Animals↗
PubMed1978

Partial purification and properties of an acid nucleotidase from the postmicrosomal supernatant of rat spleen.

1. The dephosphorylation of 3'-AMP, 3'-dAMP, 3'-CMP and 3'-dCMP was studied in the postmicrosomal supernatant of rat spleen and liver. In both organs 3'-AMP and 3'-dAMP were dephosphorylated at an appreciable rate, in both the presence and the absence of Mg(2+). The pH optimum for this dephosphorylation was in the range 4.5-5.0. 3'-CMP and 3'-dCMP were very slowly degraded, though the activity towards 3'-dCMP increased somewhat in the presence of Mg(2+). The optimum pH for this Mg(2+)-dependent dephosphorylation was 5.5-6.0. 2. The rate of dephosphorylation of 3'-AMP and 3'-dAMP per mg of protein was about 5 times as high in spleen as in liver. 3. The dephosphorylation of 3'-AMP could be ascribed to a single enzyme with pH optimum about 4.5. The activity towards 3'-dAMP could be resolved into one component coinciding with the 3'-dAMP-degrading enzyme, and one Mg(2+)-requiring component probably identical with the soluble deoxyinosine-activated nucleotidase. The dephosphorylation of 3'-dCMP seemed to be performed only by the latter enzyme. 4. The enzyme dephosphorylating 3'-AMP was purified 200-fold from the postmicrosomal supernatant and its physical and catalytic properties were compared with those of acid nucleotidase (EC 3.1.3.31) purified from rat liver lysosomes. The two enzymes were identical in all properties tested (substrate specificity, K(m), molecular weight, response to phosphatase inhibitors), but some of the data differed from earlier reports on the acid nucleotidase. 5. The subcellular localization of the acid nucleotidase, its relationship to the acid phosphatase(s) and its role in the breakdown of nucleic acid constituents are discussed.

Adenosine Monophosphate↗
PubMed2003

Cobalt activation of Escherichia coli 5'-nucleotidase is due to zinc ion displacement at only one of two metal-ion-binding sites.

Escherichia coli 5'-nucleotidase activity is stimulated 30- to 50-fold in vitro by the addition of Co(2+). Seven residues from conserved sequence motifs implicated in the catalytic and metal-ion-binding sites of E. coli 5'-nucleotidase (Asp(41), His(43), Asp(84), His(117), Glu(118), His(217) and His(252)) were selected for modification using site-directed mutagenesis of the cloned ushA gene. On the basis of comparative studies between the resultant mutant proteins and the wild-type enzyme, a model is proposed for E. coli 5'-nucleotidase in which a Co(2+) ion may displace the Zn(2+) ion at only one of two metal-ion-binding sites; the other metal-ion-binding site retains the Zn(2+) ion already present. The studies reported herein suggest that displacement occurs at the metal-ion-binding site consisting of residues Asp(84), Asn(116), His(217) and His(252), leading to the observed increase in 5'-nucleotidase activity.

5'-Nucleotidase↗
PubMed1989

Inhibition of IMP-specific cytosolic 5'-nucleotidase and adenosine formation in rat polymorphonuclear leucocytes by 5'-deoxy-5'-isobutylthio derivatives of adenosine and inosine.

1. The partially purified IMP-specific cytosolic 5'-nucleotidases from rat liver, polymorphonuclear leucocytes and heart were inhibited by 50% by 2-6 mM-5'-deoxy-5'-isobutylthioadenosine (IBTA) or 7-10 mM-5'-deoxy-5'-isobutylthioinosine (IBTI). IBTA and IBTI inhibited the rat liver and polymorphonuclear-leucocyte enzymes non-competitively. IBTA, but not IBTI, also inhibited the ecto-5'-nucleotidase of polymorphonuclear leucocytes. IBTI was, by contrast, a more potent inhibitor than IBTA of the AMP-specific soluble 5'-nucleotidase from pigeon heart. 2. During 2-deoxyglucose-induced ATP-catabolism in rat polymorphonuclear leucocytes, adenosine formation was inhibited by approx. 80% by 3 mM-IBTA and by approx. 70% by 7 mM-IBTI. 3. The results show that 5'-modified nucleosides are inhibitors of cytosolic 5'-nucleotidases and that they penetrate to inhibit their target enzymes in intact cells. Such inhibitors may be useful to clarify the mechanisms of adenosine formation and to prevent mononucleotide hydrolysis during ATP breakdown.

5'-Nucleotidase↗
PubMed1991

Association of the HNK-1 epitope with 5'-nucleotidase from Torpedo marmorata (electric ray) electric organ.

5'-Nucleotidase isolated from the electric organ of the electric ray (Torpedo marmorata) has a molecular mass of 62 kDa and, on two-dimensional electrophoresis, separates into up to 13 isoforms within a pI range of 5.9-6.7. The N-terminal sequence data show a 71% identity over 17 amino acids with that previously published for the rat liver enzyme. All forms of 5'-nucleotidase are recognized by the HNK-1 monoclonal antibody. HNK-1 immunoreactivity is found at the surface of the Schwann-cell processes covering the synaptic terminals and in this respect corresponds to that of 5'-nucleotidase in the same tissue. Since a number of glycoproteins involved in cell recognition and cell adhesion carry the HNK-1 epitope, 5'-nucleotidase may play a role in cell-cell or cell-extracellular matrix interaction in addition to its activity as an enzyme.

5'-Nucleotidase↗