Purification of 5'-nucleotidase from human seminal plasma.

5'-Nucleotidase from human seminal plasma was purified to electrophoretic homogeneity and some of its kinetic and molecular properties compared with those of 5'-nucleotidase from bull seminal plasma. The purification of the enzyme was achieved by using the same affinity chromatography media (Con A-Sepharose and AMP-Agarose or ADP-Agarose) previously used for the purification of bull seminal plasma 5'-nucleotidase (Fini, C., Ipata, P.L., Palmerini, C.A. and Floridi, A. (1983) Biochim. Biophys. Acta 748, 405-412). However, in the present purification procedure no detergent was used as it had been necessary for the purification of the bovine enzyme. The experimental data reveal some main differences between these two enzymes; first, the human enzyme seems to be constituted of a single polypeptide chain of about 71 kDa, while the 5'-nucleotidase of bull seminal plasma, in non denaturing detergent solutions, is a homodimer of about 160 kDa. Another most remarkable difference is that the human enzyme does not seem to contain a phosphatidylinositol anchoring system like the one present in the bovine enzyme and in 5'-nucleotidase of different sources (Low, M.G. (1987) Biochem. J. 244, 1-13). Finally, the AMPase activity of 5'-nucleotidase from human seminal plasma is not affected by dithiothreitol which, on the contrary, is a powerful inhibitor of the bovine enzyme causing the dissociation of its subunits which are held together by disulphide bridges (Fini, C., Minelli, A., Camici, M. and Floridi, A. (1985) Biochem. Biophys. Acta 827, 403-409).     

Immunologically distinct isoforms of ecto-5'-nucleotidase in nerve terminals of different areas of the rat hippocampus

Ecto-5'-nucleotidase is regarded as being the key enzyme in the formation of the neuromodulator adenosine from released ATP. However, the association of ecto-5'-nucleotidase with nerve terminals is not consensual. Only enzyme histochemical and biochemical studies, but not immunocytochemical studies, agree on a general synaptic location of the enzyme. To clarify this issue further we tested the effect of an antibody against ecto-5'-nucleotidase, previously used in immunocytochemical studies, on the activity of ecto-5'-nucleotidase in fractions of nerve terminals isolated from different areas of rat hippocampus. The specific activity of extracellular AMP catabolism was higher in synaptosomes from the CA3 area (0.81+/-0.06 nmol/min/mg of protein) than from synaptosomes from the CA1 area or the dentate gyrus or from the whole hippocampus (0.49-0.68 nmol/ min/mg of protein). The catabolism of AMP (10 microM) was equally inhibited (85-92%) in synaptosomes from whole hippocampus, CA1, CA3, or dentate gyrus by alpha,beta-methylene-ADP (100 microM) and equally unaffected by p-nitrophenyl phosphate (0.5 mM) or rabbit IgGs (100 microg/ml). However, the antiserum against ecto-5'-nucleotidase (100 microg/ml) inhibited extracellular AMP catabolism by 44% in CA3 synaptosomes but had little or no effect in synaptosomes from CA1, dentate gyrus, or whole hippocampus. A similar difference in the inhibitory potential of the antibody was observed between fractions of isolated 5'-nucleotidase binding to concanavalin A-Sepharose (70%) and fractions not retained by the lectin column (18%). Taken together, these results suggest that immunological isoforms of ecto-5'-nucleotidase exist in the rat hippocampal nerve terminals, with predominance in the CA3 area.     

Purification of 5'-nucleotidase from human placenta after release from plasma membranes by phosphatidylinositol-specific phospholipase C

5'-Nucleotidase was purified greater than 1000-fold from human placenta by treatment of plasma membranes with S. aureus phosphatidylinositol-specific phospholipase C and affinity chromatography on Con A Sepharose and AMP-Sepharose. The resulting enzyme had a specific activity of greater than 5000 mumol/hr/mg protein and a subunit molecular weight of 73,000. Goat antibodies against 5'-nucleotidase inhibited enzyme activity and detected 5'-nucleotidase after Western blotting. These antibodies also recognized a soluble form of 5'-nucleotidase and residual membrane-bound 5'-nucleotidase which could not be released by phosphatidylinositol-specific phospholipase C treatment, suggesting that the three forms of the enzyme are structurally related. The soluble 5'-nucleotidase may be derived from the membrane-bound form by the action of an endogenous phospholipase C. The structural basis for the inability of some of the membrane-bound 5'-nucleotidase to be released by phosphatidylinositol-specific phospholipase C is unknown.     

Purification of bovine liver cytosolic 5'-nucleotidase. Kinetic and structural studies as compared to the membrane isoenzyme

Cytosolic 5'-nucleotidase from bovine liver has been purified to homogeneity. Two affinity chromatographies on concanavalin A and 5'AMP-Sepharose columns result in a 12,000-fold purification. The sequential elution of glycoproteins from the concanavalin-A-Sepharose column with methyl alpha-D-glucoside and methyl alpha-D-mannoside greatly increases the degree of purification of the enzyme. Polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate shows two subunits having apparent molecular masses of 65 kDa and 57 kDa respectively, while only one band at 70 kDa is observed in the case of the membrane-bound 5'-nucleotidase. Both the Stokes radii, measured by gel exclusion HPLC, and the sedimentation coefficient, determined by density gradient ultracentrifugation, indicate that the cytosolic enzyme is a heterodimer of about 130 kDa. This contrasts with the membrane-bound 5'-nucleotidase which is a homodimer of 140 kDa. Moreover, the antibodies raised against the membrane 5'-nucleotidase inhibited the cytosolic form indicating that a common antigenic determinant(s) exists between the two isoenzymes. However, structural differences are revealed by immunoblotting. In the same way, the effect of lectins suggests that differences in the structure of the carbohydrate chains exist between the two isoenzymes. The purified cytosolic enzyme has lower affinity for the nucleotides than does the membrane enzyme. In addition, while ADP, [alpha,beta-CH2]ADP and ATP were strong competitive inhibitors of the membrane enzyme, ADP and ATP activate the cytosolic form and [alpha,beta-CH2]ADP has no effect. Moreover, two pH optima at 7.5 and 9.5 are observed in the cytosolic enzyme while only one at 7.5 occurred in the membrane form. Finally the exogenous cations, MgCl2 and MnCl2, are necessary for the maximal activity of the cytosolic but not of the membrane 5'-nucleotidase. All these observations indicate that the two isoenzymes are different.     

Inhibition of lymphocyte 5'-nucleotidase by lectins: effects of lectin specificity and cross-linking ability

5'-Nucleotidase, an integral glycoprotein enzyme of the lymphocyte plasma membrane, is inhibited cooperatively by the lectin concanavalin A. Because divalent succinyl-concanavalin A is a poor enzyme inhibitor, both binding and lectin-induced cross-linking of 5'-nucleotidase may be necessary for inhibition. Succinyl-concanavalin A does not compete with concanavalin A for binding to the enzyme; however, maleyl-concanavalin A, another poor inhibitor, competes effectively with the parent lectin. Thus, maleyl-concanavalin A binds to the same site as concanavalin A but causes little inhibition, whereas succinyl-concanavalin A does not bind to this site. The monovalent lectin from Ricinus communis (RCA-60) is a more effective enzyme inhibitor than the related divalent lectin (RCA-120), and inactivation of the second low-affinity sugar binding site on RCA-60 does not abolish inhibition, suggesting that multivalent cross-linking is not required for 5'-nucleotidase inhibition. Peanut and wheat germ agglutinins do not inhibit the enzyme, whereas lectins from lentil, pea, soybean, Griffonia simplicifolia, and Phaseolus vulgaris inhibit 5'-nucleotidase with various degrees of effectiveness. The only lectin showing strong positive cooperativity in its interaction with 5'-nucleotidase is concanavalin A.     

Isolation and characterization of 5'-nucleotidase of a human pancreatic tumor cell line

5'-Nucleotidase of a human pancreatic tumor cell line (PaTu II) has been purified to homogeneity after extraction with detergent followed by two affinity chromatographic steps. Sodium dodecyl sulphate polyacrylamide gel electrophoresis of purified 5'-nucleotidase revealed a single polypeptide band of 67 kDa. The Western blotted enzyme can be overlaid with concanavalin A proving its glycoprotein nature. After treatment with endoglycosidase F the deglycosylated 5'-nucleotidase exhibits an apparent molecular mass of 58 kDa. The kinetic properties of the solubilized enzyme have been determined (Km (AMP) of 4.0 microM; Vmax (AMP) = 8.6 muMOL/min.mg). Adenosine 5'-[alpha,beta-methylene]diphosphate is a competitive inhibitor of 5'-nucleotidase, whereas concanavalin A inhibits the enzymatic activity in a non-competitive manner. Polyclonal antibodies against purified 5'-nucleotidase of PaTu II have been produced which inhibit its enzymatic activity. Polyclonal antibodies raised against the enzyme purified from rat liver or bull seminal plasma also recognize 5'-nucleotidase of PaTu II cells, whereas polyclonal and monoclonal antibodies against the enzyme derived from chicken gizzard show no cross-reactivity. 5'-Nucleotidase appears to be concentrated in the plasma membrane of PaTu II cells as judged by cell fractionation and indirect immunofluorescence studies.     

Monoclonal antibodies against 5'-nucleotidase from a human pancreatic tumor cell line: their characterization and inhibitory capacity on tumor cell adhesion to fibronectin substratum.

Four mouse monoclonal antibodies (PTN63, PTN108, PTN124, PTN514) against the ecto-5'-nucleotidase purified from a human pancreatic adenocarcinoma cell line (PaTu II) have been raised and characterized. All four monoclonal antibodies recognize the protein moiety of the glycosylated ecto-5'-nucleotidase. In competition assays it was demonstrated that three of the antibodies (PTN63, PTN108, PTN514) recognize different epitopes within the protein moiety. Furthermore, PTN108, PTN124, and PTN514 reduced the 5'-nucleotidase AMPase activity in contrast to PTN63 having no inhibitory effect. The antibodies show no cross-reactivity with ecto-5'-nucleotidases from rat liver, bull seminal plasma, chicken gizzard and human peripheral blood cells. When assayed by indirect immunofluorescence the antibodies react with the plasma membrane of human pancreatic tumor cells with varying staining intensity. Immunocytochemistry on paraffin sections of normal human pancreas revealed a prominent staining of the pancreatic duct cells. No staining of the acinar and islet cells could be detected. Thus, 5'-nucleotidase is a marker enzyme for pancreatic duct cells and can be used to determine the origin of pancreatic tumor cells. PTN63 reduced the attachment to fibronectin substratum of a human pancreatic adenocarcinoma tumor cell line possessing a high amount of plasma membrane bound ecto-5'-nucleotidase, but had no effect on a cell line lacking the membrane bound AMPase. In contrast, PTN108 and PTN514, which inhibit the AMPase activity, exhibited no influence on the adhesion of human pancreatic tumor cells to fibronectin substratum.     

Evidence for the direct interaction of chicken gizzard 5'-nucleotidase with laminin and fibronectin

The ectoenzyme 5'-nucleotidase purified from chicken gizzard is shown to specifically interact with laminin and fibronectin, components of the extracellular matrix, by a number of different techniques: (i) cosedimentation with laminin by sucrose gradient centrifugation; (ii) affinity adsorption to both laminin- and fibronectin-Sepharose 4-B; (iii) specific binding to both laminin and fibronectin dotted onto cellulose filters; and (iv) monoclonal antibodies against 5'-nucleotidase are shown to interfere with the interaction of 5'-nucleotidase with laminin and fibronectin. For all the techniques employed, the interactions were found to be specific, since 5'-nucleotidase did not bind to unrelated proteins such as bovine serum albumin or to monomeric actin. The interaction of purified chicken gizzard 5'-nucleotidase could be demonstrated for the hydrophobic enzyme solubilized in detergent and after its reconstitution into artificial phospholipid vesicles. The affinity adsorption experiments indicate that reconstituted enzyme binds more strongly to both laminin and fibronectin. The 5'-nucleotidase employed in this study is anchored to the plasma membrane by a glycan-phosphatidylinositol linker. After treatment with phosphatidylinositol-specific phospholipase C, the enzyme is transformed into a hydrophilic form, for which interactions with laminin and fibronectin could also be demonstrated by the dot-blot technique. Thus controlled cleavage of the phosphatidylinositol linker of 5'-nucleotidase could enable cells to rapidly alter their adhesiveness to certain components of the extracellular matrix.     

Polyclonal and monoclonal antibodies against chicken gizzard 5′-nucleotidase inhibit the spreading process of chicken embryonic fibroblasts on laminin substratum

Polyclonal and monoclonal antibodies raised against chicken gizzard 5'-nucleotidase were tested in adhesion assays of embryonic chicken fibroblasts (CEF) for their ability to interfere with the adhesion process of these cells on either laminin or fibronectin substrata. The initial attachment process of CEF on fibronectin and laminin substrata was not influenced by preincubating these cells with antibodies against chicken gizzard 5'-nucleotidase. However, the subsequent spreading process of these cells was found to be inhibited for at least 2 h on a laminin substratum. This effect was obtained with a polyclonal antibody as well as with one from 12 monoclonal antibodies raised against the native enzyme purified from chicken gizzard. In vitro assays demonstrated a competition of laminin and this monoclonal antibody for the binding site on purified 5'-nucleotidase. Spreading-arrested and rounded CEF do not develop prominent intracellular stress-fibers like control cells, instead they seem to concentrate their available actin in areas of presumptive initial contact with the laminin substratum.     

5'-nucleotidase from the electric ray electric lobe. Primary structure and relation to mammalian and procaryotic enzymes.

A cDNA encoding a 5'-nucleotidase was identified by screening a lambda gt10 cDNA library from the electric lobe of Discopyge ommata using a cDNA probe containing the complete open reading frame coding for the rat liver enzyme. Nucleotide sequence analysis defines an open reading frame of 577 amino acids, corresponding to a calculated molecular mass of 63,833 Da. The N-terminus of the mature protein, as determined by direct protein sequencing, is preceded by 29 amino acid residues comprising a signal peptide. The C-terminus contains a stretch of hydrophobic amino acids, considered to be cleaved on post-translational modification and exchanged for glycosylphosphatidylinositol as a membrane anchor. The predicted protein contains four potential N-linked glycosylation sites. Electric ray 5'-nucleotidase shares 61% amino acid identity with the enzymes from rat liver and human placenta, and about 23% with bacterial proteins possessing 5'-nucleotidase activity and also additional enzyme activities like UDP-glucose hydrolase. Polyclonal antibodies raised against 5'-nucleotidase from mammalian sources or the electric ray electric organ reveal mutual cross-reactivity. Interestingly, there are 5-7 domains highly conserved in procaryotes and vertebrates in enzymes exhibiting 5'-nucleotidase, 3'-nucleotidase or phosphodiesterase activity. 5'-nucleotidase isolated from Torpedo electric organ hydrolyzes UDP-glucose at 8% of the rate of AMP hydrolysis. The possible phylogenetic origin of vertebrate 5'-nucleotidase from multifunctional nucleotide hydrolases is discussed.     

Vanadate inhibits degradation of short-lived, but not of long-lived, proteins in L-132 human cells.

We have analysed the membrane anchorage of plasma-membrane 5'-nucleotidase, an ectoenzyme which can mediate binding to components of the extracellular matrix. We demonstrated that the purified enzyme obtained from chicken gizzard and a human pancreatic adenocarcinoma cell line were both completely transformed into a hydrophilic form by treatment with phospholipases C and D, cleaving glycosylphosphatidylinositol (GPI). These data indicate the presence of a glycolipid linker employed for membrane anchoring of the 5'-nucleotidase obtained from both sources. Incubation of plasma membranes under identical conditions revealed that about half of the AMPase activity was resistant to GPI-hydrolysing phospholipases. Investigation of the enzymic properties of purified chicken gizzard 5'-nucleotidase revealed only minor changes after removal of the phosphatidylinositol linker. However, cleavage of the membrane anchor resulted in an increased sensitivity towards inhibition by concanavalin A. After tissue fractionation, chicken gizzard 5'-nucleotidase could be obtained as either a membrane-bound or a soluble protein; the latter is suspected to be released from the plasma membrane by endogenous phospholipases. Higher-molecular-mass proteins immuno-cross-reactive with the purified chicken gizzard 5'-nucleotidase were detected as both soluble and membrane-bound forms.     

Enzymatic activity and in vivo distribution of 5'-nucleotidase, an extracellular matrix binding glycoprotein, during the development of chicken striated muscle.

The ecto-enzyme 5'-nucleotidase isolated from chicken gizzard has previously been shown to be a potent ligand of two glycoproteins of the extracellular matrix, namely fibronectin and laminin. Using immunofluorescent labeling techniques we observed that 5'-nucleotidase codistributed with laminin during the development of chicken striated muscle. In contrast, ecto-5'-nucleotidase was only faintly detectable on cells surrounded by a matrix expressing high levels of fibronectin. This distribution pattern distinguished 5'-nucleotidase from the pluripotent extracellular matrix receptors, chicken beta 1-integrins, which are expressed equally well in muscle and connective tissue. In addition, the specific activity of striated muscle ecto-5'-nucleotidase was stable during development and increased markedly posthatching. At each age considered, this specific activity corresponded to an 80-kDa enzyme which was inhibited by alpha,beta-methyleneadenosine diphosphate or by a monoclonal antibody directed against the smooth muscle isoform of the enzyme. Previous in vitro studies have revealed that 5'-nucleotidase is involved in the spreading of various mesenchyme-derived cells, such as chicken embryonic fibroblasts and myoblasts, on a laminin substrate. A prerequisite to examining a potential in vivo role for 5'-nucleotidase as an extracellular matrix ligand was to study its distribution. In adult muscle, 5'-nucleotidase displayed a more restricted distribution than in embryo. Results show that, in vivo, 5'-nucleotidase is revealed by immunofluorescent labeling using poly- and monoclonal antibodies to chicken gizzard 5'-nucleotidase in two structures, the costameres and myotendinous junctions, which are closely related to the focal adhesion sites observed in cell culture.     

Absence of 5'-nucleotidase in porcine polymorphonuclear leucocyte membranes

A fraction enriched in plasma membranes from porcine polymorphonuclear leucocytes, isolated by sucrose density centrifugation was shown to possess considerable AMP hydrolysing activity (150 nmol/min per mg protein). However all of this activity could be inhibited using excess p-nitrophenyl phosphate in the incubation medium. Furthermore the hydrolysis of AMP by the membrane was unaffected by the 5'-nucleotidase inhibitor alpha, beta-methyleneadenosine diphosphate and by the lectin concanavalin A, another potent inhibitor of 5'-nucleotidase. An antibody against mouse liver 5'-nucleotidase also did not inhibit the activity. These results suggest that the hydrolysis of AMP by porcine polymorph membranes is not accomplished by a specific 5'-nucleotidase and the necessity for distinguishing between true 5'-nucleotidase and non-specific phosphatase activity is discussed.     

The existence and properties of two dimers of rat liver ecto-5''-nucleotidase.

Immunoaffinity-purified rat liver 5'-nucleotidase contained two subunits of Mr 70 000 (alpha) and 38 000 (beta). Charge-shift electrophoresis and chemical cross-linking revealed that approx. 80% of the solubilized enzyme activity occurred as an alpha alpha-dimer of Mr 140 000. The remaining 20% was an alpha beta-dimer of Mr 108 000. The beta-subunit did not possess enzymic activity. Peptide mapping and immunoblotting with antibodies against the alpha- and beta-subunits showed that the beta-subunit was homologous with a part of the alpha-subunit. Three monoclonal antibodies against rat liver 5'-nucleotidase were characterized as binding to the extracellular domain of the enzyme. All three monoclonal antibodies and concanavalin A bound to the alpha-subunit, but no binding could be detected to the beta-subunit. It was therefore concluded that the beta-subunit was a fragment of an alpha-subunit that had lost an extracellular domain. Both forms of the enzyme occurred in freshly solubilized membrane preparations as well.     

Evidence for an essential arginyl residue in bovine milk gamma-glutamyltransferase

Treatment of bovine milk gamma-glutamyltransferase with 2,3-butanedione in borate buffer markedly inactivates its gamma-glutamyltransferase activity. Inactivation is prevented by a combination of the gamma-glutamyl donor and acceptor substrates, glutathione, and glycylglycine, but less effectively by only one of them. Serine plus borate of maleate provides no protection against the inactivation. Amino acid analysis of the enzyme treated with butanedione in the presence and absence of the protecting substrate combination indicates that complete inactivation correlates with the modification of a single arginyl residue per molecule. The residue modified is associated with the smaller subunit of the two equal subunits which comprise the enzyme. The butanedione-treated enzyme retains a hydrolytic activity, another but less significant catalytic function of the enzyme. The results indicate that the arginyl residue is involved in recognizing the anionic moiety of the acceptor and in binding it to the acceptor site located on the smaller subunit of the enzyme.     

5'-Nucleotidase in rat liver lysosomes

5'-Nucleotidase was found in purified rat liver tritosomes. When tritosomes were subfractionated into the membrane and soluble contents fractions, 73% of the total 5'-nucleotidase activity was found in the membrane fraction and 24% in the soluble contents fraction. Immunoblotting using specific polyclonal antibodies against the rat liver plasma membrane 5'-nucleotidase showed that the mobilities on SDS-polyacrylamide gel electrophoresis of both 5'-nucleotidases in the membrane and contents fractions were identical to that of the enzyme in the plasma membranes (Mr = 72,000). 5'-Nucleotidases in the membrane and contents fractions were sensitive to neuraminidase and converted into a form that was 4 kDa smaller after digestion, as observed in the case of plasma membrane enzyme. 5'-Nucleotidases, both from the membrane and contents fractions, were purified using immunoaffinity chromatography, and the isoelectric points, heat stability, and oligomeric structure of the purified enzymes were compared. Isoelectric focusing and the heat stability test indicated the resemblance of the soluble enzyme to the membrane-bound enzyme. However, the membrane-bound enzyme aggregated in the absence of Triton X-100, whereas the soluble enzyme behaved as a dimer. The topography of 5'-nucleotidase in the tritosomal membranes was studied using antibodies against 5'-nucleotidase and neuraminidase treatment. The inhibition of 5'-nucleotidase were not observed in the intact tritosomal fraction until the tritosomes had been disrupted by osmotic shock. These results show that the active sites and the oligosaccharide chains of 5'-nucleotidase are located on the inside surface of the tritosomal membranes.     

Topographical separation of the catalytic sites of asparagine synthetase explored with monoclonal antibodies

Monoclonal antibodies which inhibited the enzymatic activity of bovine pancreatic asparagine synthetase were mapped to two topographically separate regions of the enzyme surface using competitive binding assays. Three antibodies which all inhibited glutamine- and NH3-dependent synthesis of asparagine bound to a common antigenic region. A fourth monoclonal antibody which interfered with glutamine binding or cleavage but not with NH3-dependent synthesis of asparagine was mapped to a separate region of the enzyme surface. These findings suggest a topographical separation between the aspartyl-AMP and glutamine-binding sites of bovine pancreatic asparagine synthetase. Three noninhibitory antibodies exhibited conformation-dependent binding and were mapped to a third region of the enzyme. Binding assays were used to demonstrate extensive cross-reaction of these antibodies with asparagine synthetases isolated from bovine liver and sheep pancreas. Substantial cross-reactions were also seen with the enzyme isolated from rat liver or pancreas, a human tumor cell line, and a mouse tumor cell line. Of the four antibodies that inhibited glutamine- and NH3-dependent synthesis of asparagine from ruminant species, only one bound to and inhibited the enzyme from rat liver or mouse cells, which suggests significant structural differences between the ruminant and rodent enzymes.     

Distribution of 5'-nucleotidase in muscle of some marine fishes.

A preliminary examination for the purification and characterization of 5'-nucleotidase of fish muscle was carried out and the following results were obtained. 1. The activities of 5'-nucleotidase in the muscles of marine vertebrates and invertebrates (total 11 species) were determined. The highest activity of 5'-nucleotidase was found in Blackrock fish Sebastes inermis, which was then used as a material for estimation of subcellular distribution and solubilization of the enzyme. 2. The 5'-nucleotidase of ordinary muscle of the fish Sebastes inermis was found in nuclear, microsomal and cytosolic fractions. About half of the total activity was found in the nuclear fraction, whereas the highest specific activity was observed in the microsomal fraction. 3. Complete solubilization of the enzyme was attained by using a high concentration of detergent such as Triton X-100, CHAPS, octylglucoside, octylthioglucoside and sodium deoxycholate, suggesting that the enzyme was tightly bound to the membrane. 4. Based on the results of solubility and stability tests, Triton X-100 seemed suitable for solubilizing 5'-nucleotidase from the membrane. 5. Microsomal 5'-nucleotidase was an Mg(2+)-activated enzyme, and no inactivation was observed up to 50 mM of Mg2+.     

Isolation and characterization of a Golgi-rich fraction from the adrenal medulla.

1. A Golgi-rich fraction from bovine adrenal medulla was isolated by centrifugation through discontinuous sucrose density gradients. 2. The specific activity of UDPgalactose-N-acetylglucosamine galactosyl transferase was increased in this fraction. Therefore, this enzyme is a useful marker for Golgi in bovine adrenal medulla. 3. Golgi membranes were reasonably free from mitochondria, lysosomes, endoplasmic reticulum and chromaffin granules as shown by the relatively low activities of marker enzymes. 4. The negative staining techniques of electron microscopy revealed the presence of a system of tubules, vesicles and plate-like center regions which are similar to those structures previously described of the Golgi fraction isolated from the liver. 5. The specific activity of 5'-nucleotidase in the Golgi-rich fraction was 3.5 times greater than that in adrenal homogenates. However, the subcellular distribution patterns of galactosyl transferase and 5'-nucleotidase were similar. The possibility that 5'-nucleotidase might be a conspicious component of the Golgi apparatus is discussed.     

A family of phosphohydrolases from bovine intestinal mucosa: 5'-nucleotidase

Bovine intestinal 5'-nucleotidase has been partially purified and characterized for comparison with two other phosphohydrolases from the same tissue, alkaline phosphatase and 5'-nucleotide phosphodiesterase, which are closely related structurally and mechanistically. Kinetic studies with a variety of nucleotides and phosphonate analogs show that, although 5'-nucleotidase is a monoesterase like alkaline phosphatase, it more closely resembles 5'-nucleotide phosphodiesterase in its high affinity and specificity for nucleotide binding. 5'-Nucleotidase is bound very strongly by an affinity column containing a bound phosphonate analog of ADP but is not bound by an affinity column containing a non nucleotide phosphonate which selectively binds alkaline phosphatase. 5'-Nucleotidase is strongly bound by immobilized antibodies prepared against 5'-nucleotide phosphodiesterase, and is less strongly bound by immobilized antibodies prepared against alkaline phosphatase. We conclude that 5'-nucleotidase is structurally more similar to 5'-nucleotide phosphodiesterase than to another monoesterase, alkaline phosphatase.