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Schweikert K, Burritt DJ. Polyamines in macroalgae: advances and future perspectives. JOURNAL OF PHYCOLOGY 2015; 51:838-849. [PMID: 26986881 DOI: 10.1111/jpy.12325] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2014] [Accepted: 06/04/2015] [Indexed: 06/05/2023]
Abstract
Polyamines (PA) are ubiquitous, small, aliphatic cations found in all living cells. In recent years the importance of these molecules for macroalgae has become evident and a substantial body of knowledge has been accumulated over the last three decades. This review summarizes research on the PAs found in macroalgae, their transport and metabolism, and their biological significance in processes such as cell division, chloroplast development, and reproduction. The involvement of PAs in environmental stress responses in macroalgae is also addressed. The discussion of PAs in this review not only demonstrates that PAs play an important role in physiological processes in macroalgae, but also clearly demonstrates the similarities and differences between PA metabolism in macroalgae and higher plants. Key areas for future research are also discussed.
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Affiliation(s)
- Katja Schweikert
- Department of Botany, University of Otago, P.O. Box 56, Dunedin, 9054, New Zealand
| | - David J Burritt
- Department of Botany, University of Otago, P.O. Box 56, Dunedin, 9054, New Zealand
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2
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Siu KKW, Asmus K, Zhang AN, Horvatin C, Li S, Liu T, Moffatt B, Woods VL, Howell PL. Mechanism of substrate specificity in 5'-methylthioadenosine/S-adenosylhomocysteine nucleosidases. J Struct Biol 2010; 173:86-98. [PMID: 20554051 DOI: 10.1016/j.jsb.2010.06.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2010] [Revised: 06/02/2010] [Accepted: 06/02/2010] [Indexed: 10/19/2022]
Abstract
5'-Methylthioadenosine/S-adenosylhomocysteine (MTA/SAH) nucleosidase (MTAN) plays a key role in the methionine-recycling pathway of bacteria and plants. Despite extensive structural and biochemical studies, the molecular mechanism of substrate specificity for MTAN remains an outstanding question. Bacterial MTANs show comparable efficiency in hydrolyzing MTA and SAH, while the plant enzymes select preferentially for MTA, with either no or significantly reduced activity towards SAH. Bacterial and plant MTANs show significant conservation in the overall structure, and the adenine- and ribose-binding sites. The observation of a more constricted 5'-alkylthio binding site in Arabidopsis thalianaAtMTAN1 and AtMTAN2, two plant MTAN homologues, led to the hypothesis that steric hindrance may play a role in substrate selection in plant MTANs. We show using isothermal titration calorimetry that SAH binds to both Escherichia coli MTAN (EcMTAN) and AtMTAN1 with comparable micromolar affinity. To understand why AtMTAN1 can bind but not hydrolyze SAH, we determined the structure of the protein-SAH complex at 2.2Å resolution. The lack of catalytic activity appears to be related to the enzyme's inability to bind the substrate in a catalytically competent manner. The role of dynamics in substrate selection was also examined by probing the amide proton exchange rates of EcMTAN and AtMTAN1 via deuterium-hydrogen exchange coupled mass spectrometry. These results correlate with the B factors of available structures and the thermodynamic parameters associated with substrate binding, and suggest a higher level of conformational flexibility in the active site of EcMTAN. Our results implicate dynamics as an important factor in substrate selection in MTAN.
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Affiliation(s)
- Karen K W Siu
- Research Institute, The Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada
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3
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Siu KKW, Lee JE, Sufrin JR, Moffatt BA, McMillan M, Cornell KA, Isom C, Howell PL. Molecular determinants of substrate specificity in plant 5'-methylthioadenosine nucleosidases. J Mol Biol 2008; 378:112-28. [PMID: 18342331 DOI: 10.1016/j.jmb.2008.01.088] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2007] [Revised: 01/28/2008] [Accepted: 01/30/2008] [Indexed: 10/22/2022]
Abstract
5'-Methylthioadenosine (MTA)/S-adenosylhomocysteine (SAH) nucleosidase (MTAN) is essential for cellular metabolism and development in many bacterial species. While the enzyme is found in plants, plant MTANs appear to select for MTA preferentially, with little or no affinity for SAH. To understand what determines substrate specificity in this enzyme, MTAN homologues from Arabidopsis thaliana (AtMTAN1 and AtMTAN2, which are referred to as AtMTN1 and AtMTN2 in the plant literature) have been characterized kinetically. While both homologues hydrolyze MTA with comparable kinetic parameters, only AtMTAN2 shows activity towards SAH. AtMTAN2 also has higher catalytic activity towards other substrate analogues with longer 5'-substituents. The structures of apo AtMTAN1 and its complexes with the substrate- and transition-state-analogues, 5'-methylthiotubercidin and formycin A, respectively, have been determined at 2.0-1.8 A resolution. A homology model of AtMTAN2 was generated using the AtMTAN1 structures. Comparison of the AtMTAN1 and AtMTAN2 structures reveals that only three residues in the active site differ between the two enzymes. Our analysis suggests that two of these residues, Leu181/Met168 and Phe148/Leu135 in AtMTAN1/AtMTAN2, likely account for the divergence in specificity of the enzymes. Comparison of the AtMTAN1 and available Escherichia coli MTAN (EcMTAN) structures suggests that a combination of differences in the 5'-alkylthio binding region and reduced conformational flexibility in the AtMTAN1 active site likely contribute to its reduced efficiency in binding substrate analogues with longer 5'-substituents. In addition, in contrast to EcMTAN, the active site of AtMTAN1 remains solvated in its ligand-bound forms. As the apparent pK(a) of an amino acid depends on its local environment, the putative catalytic acid Asp225 in AtMTAN1 may not be protonated at physiological pH and this suggests the transition state of AtMTAN1, like human MTA phosphorylase and Streptococcus pneumoniae MTAN, may be different from that found in EcMTAN.
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Affiliation(s)
- Karen K W Siu
- Program in Molecular Structure and Function, Research Institute, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario, Canada
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4
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Schlenk F. Methylthioadenosine. ADVANCES IN ENZYMOLOGY AND RELATED AREAS OF MOLECULAR BIOLOGY 2006; 54:195-265. [PMID: 6405586 DOI: 10.1002/9780470122990.ch4] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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5
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Schroder G, Schroder J. cDNAs for S-Adenosyl-L-Methionine Decarboxylase from Catharanthus Roseus, Heterologous Expression, Identification of the Proenzyme-Processing Site, Evidence for the Presence of Both Subunits in the Active Enzyme, and a Conserved Region in the 5' mRNA Leader. ACTA ACUST UNITED AC 1995. [DOI: 10.1111/j.1432-1033.1995.tb20231.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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6
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Choi YS, Cho YD. A new S-adenosylmethionine decarboxylase from soybean axes. BIOCHIMICA ET BIOPHYSICA ACTA 1994; 1201:466-72. [PMID: 7803479 DOI: 10.1016/0304-4165(94)90078-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
A new active S-adenosylmethionine decarboxylase (EC 4.1.1.50) (SAMDC II) was extracted from soybean (Glycine max) axes. The enzyme was purified to homogeneity by ammonium sulfate fractionation, DEAE-Sepharose and methylglyoxalbis(guanylhydrazone) (MGBG)-Sepharose 6B chromatographies. The molecular weight of the native enzyme was 110,000, while the subunit molecular weights were 66,000 and 58,000, indicating a heterodimeric structure. The Km value of the enzyme for S-adenosylmethionine was 16 microM, which is two times higher than that of previously reported S-adenosylmethionine decarboxylase (SAMDC I) (8.1 microM). The specific activity of SAMDC II during the seed growth increased rapidly and reached its maximum on the second day after germination whereas that of SAMDC I reached its peak on the fourth day. MGBG was shown to inhibit SAMDC II competitively like SAMDC I. Carbonyl and sulfhydryl group specific reagents modified SAMDC II, resulting in the loss of enzymatic activity. Agmatine, the product of arginine decarboxylation catalyzed by arginine decarboxylase, inhibited the SAMDC II competitively (Ki = 40 microM) while it inhibited the SAMDC II non-competitively (Ki = 600 mM). The possible role of the chronological appearance of SAMDC II and SAMDC I, and properties of the enzyme are briefly discussed in connection with polyamine biosynthesis in soybean axes.
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Affiliation(s)
- Y S Choi
- Department of Biochemistry, College of Science, Yousei University Seoul, Korea
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7
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Stanley B, Shantz L, Pegg A. Expression of mammalian S-adenosylmethionine decarboxylase in Escherichia coli. Determination of sites for putrescine activation of activity and processing. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)37136-3] [Citation(s) in RCA: 25] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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8
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Abstract
S-Adenosylmethionine decarboxylase (EC 4.1.1.19) was purified to homogeneity from the cytosol of soybean (Glycine max) axes by ammonium sulfate fractionation, DEAE-Sepharose and methylglyoxalbis(guanylhydrazone)-Sepharose 6B chromatographies. The enzyme was free from diamine oxidase activity. The molecular weight of the enzyme estimated by gel filtration and sodium dodecyl sulfate polyacrylamide gel electrophoresis was 66,000. The Km value for S-adenosylmethionine was 0.26 mM. The optimum pH and temperature were 7.5 and 40 degrees C. Neither putrescine nor Mg2+ affected the enzyme activity, but the enzyme was inhibited by spermidine, spermine, methylglyoxalbis(guanylhydrazone), sodium borohydride and phenylhydrazine. Agmatine was a novel inhibitor which inhibited S-adenosylmethionine decarboxylase and arginine decarboxylase, preventing the accumulation of decarboxylated S-adenosylmethionine and putrescine, respectively.
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Affiliation(s)
- Y G Yang
- Department of Biochemistry, College of Science, Yonsei University, Seoul, Korea
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9
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Furfine ES, Abeles RH. Intermediates in the conversion of 5′-S-methylthioadenosine to methionine in Klebsiella pneumoniae. J Biol Chem 1988. [DOI: 10.1016/s0021-9258(19)81558-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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10
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Della Ragione F, Oliva A, Fioretti M, Russo GL, Palumbo R, Zappia V. Physico-chemical and immunological properties of bovine liver 5'-deoxy-5'-methylthioadenosine phosphorylase. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 1988; 250:187-97. [PMID: 3151226 DOI: 10.1007/978-1-4684-5637-0_17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- F Della Ragione
- Department of Biochemistry, First Medical School, University of Naples, Italy
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11
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Cohen E, Kende H. The effect of submergence, ethylene and gibberellin on polyamines and their biosynthetic enzymes in deepwater-rice internodes. PLANTA 1986; 169:498-504. [PMID: 24232756 DOI: 10.1007/bf00392098] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/1986] [Accepted: 07/29/1986] [Indexed: 06/02/2023]
Abstract
Submergence and treatment with ethylene or gibberellic acid (GA3) stimulates rapid growth in internodes of deepwater rice (Oryza sativa L. cv. "Habiganj Aman II"). This growth is based on greatly enhanced rate of cell-division activity in the intercalary meristem (IM) and on increased cell elongation. We chose polyamine biosynthesis as a biochemical marker for cell-division activity in the IM of rice stems. Upon submergence of the plant, the activity of S-adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) in the IM increased six- to tenfold within 8 h; thereafter, SAMDC activity declined. Arginine decarboxylase (ADC; EC 4.1.1.19) showed a similar but less pronounced increase in activity. The activity of ornithine decarboxylase (ODC; EC 4.1.1.17) in the IM was not affected by submergence. The levels of putrescine and spermidine also rose in the IM of submerged, whole plants while the concentration of spermine remained low. The increase in SAMDC activity was localized in the IM while the activity of ADC rose both in the node and the IM above it. The node also contained low levels of ODC activity which increased slightly following submergence. Increased activities of polyamine-synthesizing enzymes in the nodal region of submerged plants probably resulted from the promotion of adventitious root formation in the node. Treatment of excised rice-stem sections with ethylene or GA3 enhanced the activities of SAMDC and ADC in the IM and inhibited the decline in the levels of putrescine and spermidine. We conclude that SAMDC and perhaps also ADC may serve as biochemical markers for the enhancement of cell-division activity in the IM of deepwater rice.
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Affiliation(s)
- E Cohen
- MSU-DOE Plant Research Laboratory, Michigan State University, 48824-1312, East Lansing, MI, USA
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12
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Slocum RD, Kaur-Sawhney R, Galston AW. The physiology and biochemistry of polyamines in plants. Arch Biochem Biophys 1984; 235:283-303. [PMID: 6393877 DOI: 10.1016/0003-9861(84)90201-7] [Citation(s) in RCA: 146] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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13
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Trackman PC, Abeles RH. Methionine synthesis from 5'-S-Methylthioadenosine. Resolution of enzyme activities and identification of 1-phospho-5-S methylthioribulose. J Biol Chem 1983. [DOI: 10.1016/s0021-9258(18)32277-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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14
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Guranowski AB, Chiang PK, Cantoni GL. [64] 5′-Methylthioadenosine nucleosidase (Lupinus luteus seeds). Methods Enzymol 1983. [DOI: 10.1016/s0076-6879(83)94066-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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15
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Guranowski A, Paszewski A. Metabolism of 5'-methylthioadenosine in Aspergillus nidulans. An alternative pathway for methionine synthesis via utilization of the nucleoside methylthio group. BIOCHIMICA ET BIOPHYSICA ACTA 1982; 717:289-94. [PMID: 7052140 DOI: 10.1016/0304-4165(82)90181-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Experiments in which 5'-methylthioadenosine was used as a culture supplement for methionine-requiring mutants of Aspergillus nidulans with various enzymatic lesions indicated that the methylthio group derived from the nucleoside can be recycled to methionine. The results strongly suggest that methionine may be synthesized in the reaction catalyzed by homocysteine synthase (EC 4.2.99.10) in which O-acetylhomoserine is an acceptor of the methylthio group. The first step on the salvage pathway of the methylthio group is, in Aspergillus nidulans, phosphorolytic cleavage of 5'-methylthioadenosine to adenine and 5-methylthioribose 1-phosphate catalyzed by a specific phosphorylase.
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Cone MC, Marchitto K, Zehfus B, Ferro AJ. Utilization by Saccharomyces cerevisiae of 5'-methylthioadenosine as a source of both purine and methionine. J Bacteriol 1982; 151:510-5. [PMID: 7045086 PMCID: PMC220274 DOI: 10.1128/jb.151.1.510-515.1982] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Cells of the yeast Saccharomyces cerevisiae are normally impermeable to the purine nucleosides adenosine and 5'-deoxy-5'-methylthioadenosine (MTA), a product of polyamine biosynthesis. cordycepin-sensitive, adenosine-utilizing strains of S. cerevisiae were able to use MTA to fulfill an auxotrophic requirement for purine. Cordycepin-sensitive strains carrying a met5 mutation were also able to use MTA as a source of methionine. These MTA-utilizing strains of S. cerevisiae should be useful for metabolic studies of the fate of MTA.
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17
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Backlund PS, Chang CP, Smith RA. Identification of 2-keto-4-methylthiobutyrate as an intermediate compound in methionine synthesis from 5'-methylthioadenosine. J Biol Chem 1982. [DOI: 10.1016/s0021-9258(18)34705-7] [Citation(s) in RCA: 82] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
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18
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Giovanelli J, Mudd SH, Datko AH. Recycling of methionine sulfur in a higher plant by two pathways characterized by either loss or retention of the 4-carbon moiety. Biochem Biophys Res Commun 1981; 100:831-9. [PMID: 7271784 DOI: 10.1016/s0006-291x(81)80249-5] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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Guranowski AB, Chiang PK, Cantoni GL. 5'-Methylthioadenosine nucleosidase. Purification and characterization of the enzyme from Lupinus luteus seeds. EUROPEAN JOURNAL OF BIOCHEMISTRY 1981; 114:293-9. [PMID: 6783408 DOI: 10.1111/j.1432-1033.1981.tb05148.x] [Citation(s) in RCA: 78] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
5'-Methylthioadenosine nucleosidase (EC 3.2.2.9), the enzyme which catalyzes hydrolytic cleavage of 5'-methylthioadenosine with the formation of adenine and 5'-methylthioribose, has been purified to homogeneity from Lupinus luteus seeds. The nucleosidase has a native molecular weight of 62 000 and consists of two identical subunits, as judged by gel filtration and dodecylsulfate/polyacrylamide gel electrophoresis. The nucleosidase exhibits highest specificity towards the natural substrate with a Km of 4.1 X 10(-7) M for 5'-methylthioadenosine. It does not cleave adenine from S-adenosylhomocysteine. Among the synthetic analogs of 5'-methylthioadenosine tested, eleven compounds appear to be able to substitute as substrates. Furthermore, the enzyme can liberate hypoxanthinine from six inosyl (deaminated) derivatives obtained by enzymatic deamination of 5'-methylthioadenosine and its synthetic analogs. The Km for 5'-methylthioinosine is 55 microM, and the maximal velocity about 50-times lower than for 5'-methylthioadenosine. The reaction catalyzed by the nucleosidase can be inhibited by adenine (Ki = 11 microM), 3-deazaadenine (Ki = 19 microM), and 9-erythro(2-hydroxyl-3-nonyl)adenine (ki = 37 microM).
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20
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Vandenbark AA, Ferro AJ, Barney CL. Inhibition of lymphocyte transformation by a naturally occurring metabolite: 5'-methylthioadenosine. Cell Immunol 1980; 49:26-33. [PMID: 7351031 DOI: 10.1016/0008-8749(80)90052-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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21
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Aleksijevic A, Grove J, Schuber F. Studies on polyamine biosynthesis in Euglena gracilis. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 565:199-207. [PMID: 116684 DOI: 10.1016/0005-2787(79)90096-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Euglene gracilis (strain Z) was found to contain five polyamines which could be separated by high-pressure cation-exchange chromatography. 1,3-Diaminopropane, putrescine, norspermidine (N-(3-aminopropyl)-1,3-diaminopropane), spermidine and norspermine (N,N'-bis(aminopropyl)-1,3-diaminopropane) were identified. Biosynthesis of putrescine in E. gracilis proceeds through decarboxylation of L-ornithine, no arginine decarboxylase (EC 4.1.1.19) activity could be detected. The properties of the enzymes ornithine decarboxylase (EC 4.1.1.17) and S-adenosylmethionine decarboxylase (EC 4.1.1.50) in this alga were found to be similar to those of the enzymes isolated from animal tissues or yeast cells. A bioxynthetic scheme is proposed which relates the different polyamines occurring in E. gracilis.
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Ferro AJ, Wrobel NC, Nicolette JA. 5-methylthioribose 1-phosphate: a product of partially purified, rat liver 5'-methylthioadenosine phosphorylase activity. BIOCHIMICA ET BIOPHYSICA ACTA 1979; 570:65-73. [PMID: 114225 DOI: 10.1016/0005-2744(79)90201-8] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
5'-Methylthioadenosine phosphorylase from rat liver has been purified 112-fold. A molecular weight of 90 000 for the enzyme was estimated from gel filtration on Sephadex G-150. The Km for 5'-methylthioadenosine was 4.7 . 10(-7) M, while the Km for phosphate was 2 . 10(-4) M. The products of the reaction were isolated and identified as adenine and 5-methylthioribose 1-phosphate. In addition to 5'-methylthioadenosine the nucleoside analogues 5'-ethylthioadenosine and 5'-n-propylthioadenosine also served as substrates for the enzyme. The 7-deaza analogue 5'-methylthiotubercidin was found to be an inhibitor of the reaction, but was inactive as a substrate.
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Ferro AJ, Barrett A, Shapiro SK. Kinetic properties and the effect of substrate analogues on 5'-methylthioadenosine nucleosidase from Escherichia coli. BIOCHIMICA ET BIOPHYSICA ACTA 1976; 438:487-94. [PMID: 782530 DOI: 10.1016/0005-2744(76)90264-3] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
5'-Methylthioadenosine nucleosidase (EC 3.2.2-) from Escherichia coli has been purified 220-fold. A molecular weight of 31 000 for the enzyme was estimated from gel filtration on Sephadex G-150. The Km for 5'-methylthioadenosine was 3.1-10(-7) M. In addition to 5'-methylthioadenosine, the nucleoside analogues 5'-ethylthioadenosine, 5'-n-propylthioadenosine, and S-adenosyl-homocysteine also served as substrates for the enzyme. These substrate analogues acted as competitive inhibitors of the reaction with 5'-methylthioadenosine. The Ki values for 5'-ethylthioadenosine, 5'-n-propylthioadenosine, and S-adenosylhomocysteine were determined to be 1.3-10(-7) M, 4.6-10(-8) M, and 1.92-10(-7) M respectively.
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