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A. J. Ferro - One of the best experts on this subject based on the ideXlab platform.
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5 methylthioadenosine Nucleosidase and 5 methylthioribose kinase activities in relation to stress induced ethylene biosynthesis
Physiologia Plantarum, 1992Co-Authors: Mosbah M. Kushad, A. Orvos, A. J. FerroAbstract:The activities of 5’-methylthioadenosine (MTA) Nucleosidase (EC 2.2.2.28) and 5-methylthioribose (MTR) kinase (EC 2.7.1.100) were related to changes in ethylene biosynthesis in tomato (Lycopersicon esculentum Mill. cv. Rutgers) and cucumber (Cucumis sativus Mill. cv. Poinsett 76) fruit following wounding and chemically induced stresses. Stress ethylene formation in wounded tomato and cucumber tissue continued to increase after wounding, reached its peak by 3h, and then declined. The activities of MTA Nucleosidase and MTR kinase increased parallel to stress ethylene in both tissues. At peak ethylene formation, MTA and MTR kinase activities were 2- to 4-fold higher in wounded than in intact tissue. Wounded, mature-green tomato tissue treated with specific inhibitors of MTA Nucleosidase and MTR kinase showed a significant reduction in the activities of these enzymes, which was concomitant with a decline in stress ethylene biosynthesis. When mature-green tomato discs were infiltrated with [14CH3] MTA and wounded, radioactive MTR and methionine were formed. Incubation of mature-green tomato discs with Cu2+ and Li+ in the presence of kinetin increased ethylene biosynthesis. MTA Nucleosidase activity was higher than that of the control in the presence of Cu2+ but not in the presence of Li+, while MTR kinase activity was lower than that of the control in both Cu2+ and Li+ treatments. Data indicate that MTA Nucleosidase and MTR kinase are required for wound-induced ethylene biosynthesis but not for chemical stress-induced ethylene by Cu2+ or Li+ treatments.
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5′‐Methylthioadenosine Nucleosidase and 5‐methylthioribose kinase activities in relation to stress‐induced ethylene biosynthesis
Physiologia Plantarum, 1992Co-Authors: Mosbah M. Kushad, A. Orvos, A. J. FerroAbstract:The activities of 5’-methylthioadenosine (MTA) Nucleosidase (EC 2.2.2.28) and 5-methylthioribose (MTR) kinase (EC 2.7.1.100) were related to changes in ethylene biosynthesis in tomato (Lycopersicon esculentum Mill. cv. Rutgers) and cucumber (Cucumis sativus Mill. cv. Poinsett 76) fruit following wounding and chemically induced stresses. Stress ethylene formation in wounded tomato and cucumber tissue continued to increase after wounding, reached its peak by 3h, and then declined. The activities of MTA Nucleosidase and MTR kinase increased parallel to stress ethylene in both tissues. At peak ethylene formation, MTA and MTR kinase activities were 2- to 4-fold higher in wounded than in intact tissue. Wounded, mature-green tomato tissue treated with specific inhibitors of MTA Nucleosidase and MTR kinase showed a significant reduction in the activities of these enzymes, which was concomitant with a decline in stress ethylene biosynthesis. When mature-green tomato discs were infiltrated with [14CH3] MTA and wounded, radioactive MTR and methionine were formed. Incubation of mature-green tomato discs with Cu2+ and Li+ in the presence of kinetin increased ethylene biosynthesis. MTA Nucleosidase activity was higher than that of the control in the presence of Cu2+ but not in the presence of Li+, while MTR kinase activity was lower than that of the control in both Cu2+ and Li+ treatments. Data indicate that MTA Nucleosidase and MTR kinase are required for wound-induced ethylene biosynthesis but not for chemical stress-induced ethylene by Cu2+ or Li+ treatments.
Michael K. Riscoe - One of the best experts on this subject based on the ideXlab platform.
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structural comparison of mta phosphorylase and mta adohcy Nucleosidase explains substrate preferences and identifies regions exploitable for inhibitor design
Biochemistry, 2004Co-Authors: Jeffrey E. Lee, Kenneth A. Cornell, Michael K. Riscoe, Ethan C. Settembre, Janice R. Sufrin, Steven E. Ealick, Lynne P HowellAbstract:The development of new and effective antiprotozoal drugs has been a difficult challenge because of the close similarity of the metabolic pathways between microbial and mammalian systems. 5‘-Methylthioadenosine/S-adenosylhomocysteine (MTA/AdoHcy) Nucleosidase is thought to be an ideal target for therapeutic drug design as the enzyme is present in many microbes but not in mammals. MTA/AdoHcy Nucleosidase (MTAN) irreversibly depurinates MTA or AdoHcy to form adenine and the corresponding thioribose. The inhibition of MTAN leads to a buildup of toxic byproducts that affect various microbial pathways such as quorum sensing, biological methylation, polyamine biosynthesis, and methionine recycling. The design of Nucleosidase-specific inhibitors is complicated by its structural similarity to the human MTA phosphorylase (MTAP). The crystal structures of human MTAP complexed with formycin A and 5‘-methylthiotubercidin have been solved to 2.0 and 2.1 A resolution, respectively. Comparisons of the MTAP and MTAN inhib...
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Structural comparison of MTA phosphorylase and MTA/AdoHcy Nucleosidase explains substrate preferences and identifies regions exploitable for inhibitor design.
Biochemistry, 2004Co-Authors: Jeffrey E. Lee, Kenneth A. Cornell, Michael K. Riscoe, Ethan C. Settembre, Janice R. Sufrin, Steven E. Ealick, P. Lynne HowellAbstract:The development of new and effective antiprotozoal drugs has been a difficult challenge because of the close similarity of the metabolic pathways between microbial and mammalian systems. 5‘-Methylthioadenosine/S-adenosylhomocysteine (MTA/AdoHcy) Nucleosidase is thought to be an ideal target for therapeutic drug design as the enzyme is present in many microbes but not in mammals. MTA/AdoHcy Nucleosidase (MTAN) irreversibly depurinates MTA or AdoHcy to form adenine and the corresponding thioribose. The inhibition of MTAN leads to a buildup of toxic byproducts that affect various microbial pathways such as quorum sensing, biological methylation, polyamine biosynthesis, and methionine recycling. The design of Nucleosidase-specific inhibitors is complicated by its structural similarity to the human MTA phosphorylase (MTAP). The crystal structures of human MTAP complexed with formycin A and 5‘-methylthiotubercidin have been solved to 2.0 and 2.1 A resolution, respectively. Comparisons of the MTAP and MTAN inhib...
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Structure of Escherichia coli 5'-methylthioadenosine/ S-adenosylhomocysteine Nucleosidase inhibitor complexes provide insight into the conformational changes required for substrate binding and catalysis.
The Journal of biological chemistry, 2002Co-Authors: Jeffrey E. Lee, Kenneth A. Cornell, Michael K. Riscoe, P. Lynne HowellAbstract:Abstract 5′-Methylthioadenosine/S-adenosylhomocysteine (MTA/AdoHcy) Nucleosidase is a key enzyme in a number of critical biological processes in many microbes. This Nucleosidase catalyzes the irreversible hydrolysis of the N9–C1′bond of MTA or AdoHcy to form adenine and the corresponding thioribose. The key role of the MTA/AdoHcy Nucleosidase in biological methylation, polyamine biosynthesis, methionine recycling, and bacterial quorum sensing has made it an important antimicrobial drug target. The crystal structures of Escherichia coli MTA/AdoHcy Nucleosidase complexed with the transition state analog, formycin A (FMA), and the nonhydrolyzable substrate analog, 5′-methylthiotubercidin (MTT) have been solved to 2.2- and 2.0-A resolution, respectively. These are the first MTA/AdoHcy Nucleosidase structures to be solved in the presence of inhibitors. These structures clearly identify the residues involved in substrate binding and catalysis in the active site. Comparisons of the inhibitor complexes to the adenine-bound MTA/AdoHcy Nucleosidase (Lee, J. E., Cornell, K. A., Riscoe, M. K., and Howell, P. L. (2001) Structure (Camb.) 9, 941–953) structure provide evidence for a ligand-induced conformational change in the active site and the substrate preference of the enzyme. The enzymatic mechanism has been re-examined.
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structure of e coli 5 methylthioadenosine s adenosylhomocysteine Nucleosidase reveals similarity to the purine nucleoside phosphorylases
Structure, 2001Co-Authors: Jeffrey E. Lee, Michael K. Riscoe, K A Cornell, P.l. HowellAbstract:Abstract Background: 5′-methylthioadenosine/S-adenosyl-homocysteine (MTA/AdoHcy) Nucleosidase catalyzes the irreversible cleavage of 5′-methylthioadenosine and S-adenosylhomocysteine to adenine and the corresponding thioribose, 5′-methylthioribose and S-ribosylhomocysteine, respectively. While this enzyme is crucial for the metabolism of AdoHcy and MTA nucleosides in many prokaryotic and lower eukaryotic organisms, it is absent in mammalian cells. This metabolic difference represents an exploitable target for rational drug design. Results: The crystal structure of E. coli MTA/AdoHcy Nucleosidase was determined at 1.90 A resolution with the multiwavelength anomalous diffraction (MAD) technique. Each monomer of the MTA/AdoHcy Nucleosidase dimer consists of a mixed α/β domain with a nine-stranded mixed β sheet, flanked by six α helices and a small 3 10 helix. Intersubunit contacts between the two monomers present in the asymmetric unit are mediated primarily by helix-helix and helix-loop hydrophobic interactions. The unexpected presence of an adenine molecule in the active site of the enzyme has allowed the identification of both substrate binding and potential catalytic amino acid residues. Conclusions: Although the sequence of E. coli MTA/AdoHcy Nucleosidase has almost no identity with any known enzyme, its tertiary structure is similar to both the mammalian (trimeric) and prokaryotic (hexameric) purine nucleoside phosphorylases. The structure provides evidence that this protein is functional as a dimer and that the dual specificity for MTA and AdoHcy results from the truncation of a helix. The structure of MTA/AdoHcy Nucleosidase is the first structure of a prokaryotic nucleoside N-ribohydrolase specific for 6-aminopurines.
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Structure of E. coli 5′-methylthioadenosine/S-adenosylhomocysteine Nucleosidase Reveals Similarity to the Purine Nucleoside Phosphorylases
Structure, 2001Co-Authors: Jeffrey E. Lee, Michael K. Riscoe, K A Cornell, P.l. HowellAbstract:Abstract Background: 5′-methylthioadenosine/S-adenosyl-homocysteine (MTA/AdoHcy) Nucleosidase catalyzes the irreversible cleavage of 5′-methylthioadenosine and S-adenosylhomocysteine to adenine and the corresponding thioribose, 5′-methylthioribose and S-ribosylhomocysteine, respectively. While this enzyme is crucial for the metabolism of AdoHcy and MTA nucleosides in many prokaryotic and lower eukaryotic organisms, it is absent in mammalian cells. This metabolic difference represents an exploitable target for rational drug design. Results: The crystal structure of E. coli MTA/AdoHcy Nucleosidase was determined at 1.90 A resolution with the multiwavelength anomalous diffraction (MAD) technique. Each monomer of the MTA/AdoHcy Nucleosidase dimer consists of a mixed α/β domain with a nine-stranded mixed β sheet, flanked by six α helices and a small 3 10 helix. Intersubunit contacts between the two monomers present in the asymmetric unit are mediated primarily by helix-helix and helix-loop hydrophobic interactions. The unexpected presence of an adenine molecule in the active site of the enzyme has allowed the identification of both substrate binding and potential catalytic amino acid residues. Conclusions: Although the sequence of E. coli MTA/AdoHcy Nucleosidase has almost no identity with any known enzyme, its tertiary structure is similar to both the mammalian (trimeric) and prokaryotic (hexameric) purine nucleoside phosphorylases. The structure provides evidence that this protein is functional as a dimer and that the dual specificity for MTA and AdoHcy results from the truncation of a helix. The structure of MTA/AdoHcy Nucleosidase is the first structure of a prokaryotic nucleoside N-ribohydrolase specific for 6-aminopurines.
Mosbah M. Kushad - One of the best experts on this subject based on the ideXlab platform.
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Reduced 5'-Methylthioadenosine Nucleosidase and 5-Methylthioribose Activities and Ethylene Biosynthesis in Nonripening Tomato Mutants `Rin' and `Nor' Relative to Ripening Tomato `Rutgers'
HortScience, 1996Co-Authors: Chunlin Xiao, Mosbah M. KushadAbstract:5'-methylthioadenosine (MTA) Nucleosidase (EC.2.2.2.28) and 5-methylthioribose (MTR) kinase (EC.2.7.1.100) activities were evaluated in `rin', `nor', and `Rutgers' tomato fruit during development and ripening. Changes in the activities of these enzymes were compared to ethylene biosynthesis. MTA Nucleosidase and MTR kinase activities in `rin' and `nor' were ≈30% and 22%, respectively, lower than `Rutgers' during the first 2 weeks of fruit development. In `Rutgers', activities of these enzymes declined sharply until fruit maturity. Shortly before climacteric rise in ethylene synthesis, MTA Nucleosidase, and MTR kinase activities increased, reaching a maximum level before peak ethylene synthesis then declined when fruit started to approach senescence. Whereas, `rin' and `nor' mutants exhibited no climacteric rise in ethylene synthesis and no change in MTA Nucleosidase or MTR kinase activities, following their decline after 2 weeks of growth. A rapid increase in ethylene synthesis was observed when mature green `rin' and `nor' fruit were wounded. This increase in ethylene was paralleled by an increase in MTA Nucleosidase and MTR kinase activities. However, increase in wound ethylene, MTA Nucleosidase, and MTR kinase activities in `rin' and `nor' was ≈40% less than what we had previously reported in `Rutgers'. Relationship of MTA and MTR kinase activities to fruit growth, development, ripening, and natural and wound ethylene biosynthesis will be described.
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5 methylthioadenosine Nucleosidase and 5 methylthioribose kinase activities in relation to stress induced ethylene biosynthesis
Physiologia Plantarum, 1992Co-Authors: Mosbah M. Kushad, A. Orvos, A. J. FerroAbstract:The activities of 5’-methylthioadenosine (MTA) Nucleosidase (EC 2.2.2.28) and 5-methylthioribose (MTR) kinase (EC 2.7.1.100) were related to changes in ethylene biosynthesis in tomato (Lycopersicon esculentum Mill. cv. Rutgers) and cucumber (Cucumis sativus Mill. cv. Poinsett 76) fruit following wounding and chemically induced stresses. Stress ethylene formation in wounded tomato and cucumber tissue continued to increase after wounding, reached its peak by 3h, and then declined. The activities of MTA Nucleosidase and MTR kinase increased parallel to stress ethylene in both tissues. At peak ethylene formation, MTA and MTR kinase activities were 2- to 4-fold higher in wounded than in intact tissue. Wounded, mature-green tomato tissue treated with specific inhibitors of MTA Nucleosidase and MTR kinase showed a significant reduction in the activities of these enzymes, which was concomitant with a decline in stress ethylene biosynthesis. When mature-green tomato discs were infiltrated with [14CH3] MTA and wounded, radioactive MTR and methionine were formed. Incubation of mature-green tomato discs with Cu2+ and Li+ in the presence of kinetin increased ethylene biosynthesis. MTA Nucleosidase activity was higher than that of the control in the presence of Cu2+ but not in the presence of Li+, while MTR kinase activity was lower than that of the control in both Cu2+ and Li+ treatments. Data indicate that MTA Nucleosidase and MTR kinase are required for wound-induced ethylene biosynthesis but not for chemical stress-induced ethylene by Cu2+ or Li+ treatments.
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5′‐Methylthioadenosine Nucleosidase and 5‐methylthioribose kinase activities in relation to stress‐induced ethylene biosynthesis
Physiologia Plantarum, 1992Co-Authors: Mosbah M. Kushad, A. Orvos, A. J. FerroAbstract:The activities of 5’-methylthioadenosine (MTA) Nucleosidase (EC 2.2.2.28) and 5-methylthioribose (MTR) kinase (EC 2.7.1.100) were related to changes in ethylene biosynthesis in tomato (Lycopersicon esculentum Mill. cv. Rutgers) and cucumber (Cucumis sativus Mill. cv. Poinsett 76) fruit following wounding and chemically induced stresses. Stress ethylene formation in wounded tomato and cucumber tissue continued to increase after wounding, reached its peak by 3h, and then declined. The activities of MTA Nucleosidase and MTR kinase increased parallel to stress ethylene in both tissues. At peak ethylene formation, MTA and MTR kinase activities were 2- to 4-fold higher in wounded than in intact tissue. Wounded, mature-green tomato tissue treated with specific inhibitors of MTA Nucleosidase and MTR kinase showed a significant reduction in the activities of these enzymes, which was concomitant with a decline in stress ethylene biosynthesis. When mature-green tomato discs were infiltrated with [14CH3] MTA and wounded, radioactive MTR and methionine were formed. Incubation of mature-green tomato discs with Cu2+ and Li+ in the presence of kinetin increased ethylene biosynthesis. MTA Nucleosidase activity was higher than that of the control in the presence of Cu2+ but not in the presence of Li+, while MTR kinase activity was lower than that of the control in both Cu2+ and Li+ treatments. Data indicate that MTA Nucleosidase and MTR kinase are required for wound-induced ethylene biosynthesis but not for chemical stress-induced ethylene by Cu2+ or Li+ treatments.
Kenneth A. Cornell - One of the best experts on this subject based on the ideXlab platform.
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structural comparison of mta phosphorylase and mta adohcy Nucleosidase explains substrate preferences and identifies regions exploitable for inhibitor design
Biochemistry, 2004Co-Authors: Jeffrey E. Lee, Kenneth A. Cornell, Michael K. Riscoe, Ethan C. Settembre, Janice R. Sufrin, Steven E. Ealick, Lynne P HowellAbstract:The development of new and effective antiprotozoal drugs has been a difficult challenge because of the close similarity of the metabolic pathways between microbial and mammalian systems. 5‘-Methylthioadenosine/S-adenosylhomocysteine (MTA/AdoHcy) Nucleosidase is thought to be an ideal target for therapeutic drug design as the enzyme is present in many microbes but not in mammals. MTA/AdoHcy Nucleosidase (MTAN) irreversibly depurinates MTA or AdoHcy to form adenine and the corresponding thioribose. The inhibition of MTAN leads to a buildup of toxic byproducts that affect various microbial pathways such as quorum sensing, biological methylation, polyamine biosynthesis, and methionine recycling. The design of Nucleosidase-specific inhibitors is complicated by its structural similarity to the human MTA phosphorylase (MTAP). The crystal structures of human MTAP complexed with formycin A and 5‘-methylthiotubercidin have been solved to 2.0 and 2.1 A resolution, respectively. Comparisons of the MTAP and MTAN inhib...
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Structural comparison of MTA phosphorylase and MTA/AdoHcy Nucleosidase explains substrate preferences and identifies regions exploitable for inhibitor design.
Biochemistry, 2004Co-Authors: Jeffrey E. Lee, Kenneth A. Cornell, Michael K. Riscoe, Ethan C. Settembre, Janice R. Sufrin, Steven E. Ealick, P. Lynne HowellAbstract:The development of new and effective antiprotozoal drugs has been a difficult challenge because of the close similarity of the metabolic pathways between microbial and mammalian systems. 5‘-Methylthioadenosine/S-adenosylhomocysteine (MTA/AdoHcy) Nucleosidase is thought to be an ideal target for therapeutic drug design as the enzyme is present in many microbes but not in mammals. MTA/AdoHcy Nucleosidase (MTAN) irreversibly depurinates MTA or AdoHcy to form adenine and the corresponding thioribose. The inhibition of MTAN leads to a buildup of toxic byproducts that affect various microbial pathways such as quorum sensing, biological methylation, polyamine biosynthesis, and methionine recycling. The design of Nucleosidase-specific inhibitors is complicated by its structural similarity to the human MTA phosphorylase (MTAP). The crystal structures of human MTAP complexed with formycin A and 5‘-methylthiotubercidin have been solved to 2.0 and 2.1 A resolution, respectively. Comparisons of the MTAP and MTAN inhib...
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Structure of Escherichia coli 5'-methylthioadenosine/ S-adenosylhomocysteine Nucleosidase inhibitor complexes provide insight into the conformational changes required for substrate binding and catalysis.
The Journal of biological chemistry, 2002Co-Authors: Jeffrey E. Lee, Kenneth A. Cornell, Michael K. Riscoe, P. Lynne HowellAbstract:Abstract 5′-Methylthioadenosine/S-adenosylhomocysteine (MTA/AdoHcy) Nucleosidase is a key enzyme in a number of critical biological processes in many microbes. This Nucleosidase catalyzes the irreversible hydrolysis of the N9–C1′bond of MTA or AdoHcy to form adenine and the corresponding thioribose. The key role of the MTA/AdoHcy Nucleosidase in biological methylation, polyamine biosynthesis, methionine recycling, and bacterial quorum sensing has made it an important antimicrobial drug target. The crystal structures of Escherichia coli MTA/AdoHcy Nucleosidase complexed with the transition state analog, formycin A (FMA), and the nonhydrolyzable substrate analog, 5′-methylthiotubercidin (MTT) have been solved to 2.2- and 2.0-A resolution, respectively. These are the first MTA/AdoHcy Nucleosidase structures to be solved in the presence of inhibitors. These structures clearly identify the residues involved in substrate binding and catalysis in the active site. Comparisons of the inhibitor complexes to the adenine-bound MTA/AdoHcy Nucleosidase (Lee, J. E., Cornell, K. A., Riscoe, M. K., and Howell, P. L. (2001) Structure (Camb.) 9, 941–953) structure provide evidence for a ligand-induced conformational change in the active site and the substrate preference of the enzyme. The enzymatic mechanism has been re-examined.
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Cloning and expression of Escherichia coli 5′-methylthioadenosine/S-adenosylhomocysteine Nucleosidase: Identification of the pfs gene product
Biochimica et biophysica acta, 1998Co-Authors: Kenneth A. Cornell, Michael K. RiscoeAbstract:Abstract The enzyme 5′-methylthioadenosine/S-adenosylhomocysteine Nucleosidase (EC 3.2.2.9) is responsible for cleavage of the glycosidic bond in both 5′-methylthioadenosine (MTA) and S-adenosylhomocysteine (SAH). Based on amino acid sequence analysis of this enzyme from Klebsiella, we recently speculated that an open reading frame found in E. coli (designated pfs) encoded MTA/SAH Nucleosidase. To explore this possibility, we amplified, cloned, and expressed the complete pfs gene from E. coli genomic DNA. The recombinant protein exhibited a molecular weight and Michaelis constants for MTA that are in agreement with those reported for native enzyme. From this biochemical evidence we confirm our original assignment of the pfs gene as encoding MTA/SAH Nucleosidase.
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cloning and expression of escherichia coli 5 methylthioadenosine s adenosylhomocysteine Nucleosidase identification of the pfs gene product
Biochimica et Biophysica Acta, 1998Co-Authors: Kenneth A. Cornell, Michael K. RiscoeAbstract:Abstract The enzyme 5′-methylthioadenosine/S-adenosylhomocysteine Nucleosidase (EC 3.2.2.9) is responsible for cleavage of the glycosidic bond in both 5′-methylthioadenosine (MTA) and S-adenosylhomocysteine (SAH). Based on amino acid sequence analysis of this enzyme from Klebsiella, we recently speculated that an open reading frame found in E. coli (designated pfs) encoded MTA/SAH Nucleosidase. To explore this possibility, we amplified, cloned, and expressed the complete pfs gene from E. coli genomic DNA. The recombinant protein exhibited a molecular weight and Michaelis constants for MTA that are in agreement with those reported for native enzyme. From this biochemical evidence we confirm our original assignment of the pfs gene as encoding MTA/SAH Nucleosidase.
Andrzej Guranowski - One of the best experts on this subject based on the ideXlab platform.
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Calcium-stimulated guanosine--inosine Nucleosidase from yellow lupin (Lupinus luteus).
Phytochemistry, 2006Co-Authors: Maciej Szuwart, Elżbieta Starzyńska, Małgorzata Pietrowska-borek, Andrzej GuranowskiAbstract:Guanosine-inosine-preferring nucleoside N-ribohydrolase has been purified to homogeneity from yellow lupin (Lupinus luteus) seeds by ammonium sulfate fractionation, ion-exchange chromatography and gel filtration. The enzyme functions as a monomeric, 80kDa polypeptide, most effectively between pH 4.7 and 5.5. Of various mono- and divalent cations tested, Ca(2+) appeared to stimulate enzyme activity. The Nucleosidase was activated 6-fold by 2mM exogenous CaCl(2) or Ca(NO(3))(2), with K(a)=0.5mM (estimated for CaCl(2)). The K(m) values estimated for guanosine and inosine were 2.7+/-0.3 microM. Guanosine was hydrolyzed 12% faster than inosine while adenosine and xanthosine were poor substrates. 2'-Deoxyguanosine, 2'-deoxyinosine, 2'-methylguanosine, pyrimidine nucleosides and 5'-GMP were not hydrolyzed. However, the enzyme efficiently liberated the corresponding bases from synthetic nucleosides, such as 1-methylguanosine, 7-methylguanosine, 1-N(2)-ethenoguanosine and 1-N(2)-isopropenoguanosine, but hydrolyzed poorly the ribosides of 6-methylaminopurine and 2,6-diaminopurine. MnCl(2) or ZnCl(2) inhibited the hydrolysis of guanosine with I(50) approximately 60 microM. Whereas 2'-deoxyguanosine, 2'-methylguanosine, adenosine, as well as guanine were competitive inhibitors of this reaction (K(i) values were 1.5, 3.6, 21 and 9.7 microM, respectively), hypoxanthine was a weaker inhibitor (K(i)=64 microM). Adenine, ribose, 2-deoxyribose, 5'-GMP and pyrimidine nucleosides did not inhibit the enzyme. The guanosine-inosine hydrolase activity occurred in all parts of lupin seedlings and in cotyledons it increased up to 5-fold during seed germination, reaching maximum in the third/fourth day. The lupin Nucleosidase has been compared with other Nucleosidases.
