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  • 1
    ISSN: 1432-2048
    Keywords: Key words: Ascorbate peroxidase ; cDNA ; Glycine (ascorbate peroxidase)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Screening of a cDNA library from soybean (Glycine max (L.) Merr. cv. Century) with probes based upon cytosolic ascorbate peroxidase (APx; EC 1.11.1.11) genes identified two full-length clones (SOYAPx1, SOYAPx2) apparently encoding for different soybean leaf cytosolic APxs. The deduced amino acid sequences of the two APx cDNA products differed in 13 of the 250 amino acids. The SOYAPx1 cDNA was identical to the cytosolic APx cDNA previously found in soybean root nodules. Escherichia coli expression systems were developed using both soybean APx cDNAs. Recombinant SOYAPx1 and SOYAPx2 were then utilized to characterize the enzymatic properties of the two APx cDNA products.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In the present study we determined the effects of methionine, intermediates of polyamine catabolic pathways and inhibitors of either ethylene biosynthetic or polyamine catabolic pathways on polyamine accumulation in soybean leaves. Inhibitors to SAM decarboxylase and spermidine synthase, methylglyloxal-bis-(guanylhy-drazone) and cyclohexylamine, respectively, suggest that methionine may provide aminopropyl groups for the synthesis of polyamine via S-adenosylmethionine (SAM). Results from experiments that utilized a combination of compounds which altered either ethylene or polyamine biosynthesis, namely, aminoethoxyvinyl glycine, CoSO4, 2,5-norbornadiene, and CuSO4, suggest the two pathways compete for a common precursor. However, exogenous addition of ethylene (via ethephon treatments) had little or no effect on polyamine biosynthesis. Likewise, polyamine treatments had little or no effect on ethylene biosynthesis. These data suggest that there are few or no inhibitory effects from the end products of one pathway on the synthesis of the other. Data from leaves treated with metabolic intermediates in the catabolic pathway of polyamines and inhibitors of enzymes in the catabolic pathway, i.e. aminoguanidine, hydroxyethyldrazine and gabaculine, suggest that the observed increases in polyamine titers were not due to decreased catabolism of the polyamines. One catabolic intermediate, γ-aminobutyric acid (GABA), elevated putrescine, spermidine and spermine by 12-, 1.4-, and 2-fold, respectively, Ethylene levels decreased (25%) in GABA-treated leaves. This small decrease in ethylene could not account for such large increase in putrescine titers. Further analysis demonstrated that the GABA-mediated polyamine accumulation was inhibited by difluoromethylarginine, an inhibitor of arginine decarboxylase, but not by difluoromethylornithine, an inhibitor of ornithine decarboxylase. These data suggest that GABA directly or indirectly affects the biosynthesis of polyamines via arginine decarboxylase.
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  • 3
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Soybean (Glycine max [L.] Merr. cv. Century) seedlings were germinated in vermiculite, sub-irrigated with a complete nutrient solution, without nitrogen or supplemented with 10 mM KNO3, 5 mM (NH4)2SO4, or 5 mM NH4NO3. After 14 days in the light, or 5 days in the dark, tissues from different organs were harvested separately. Similarly, tissues from different organs from 14- or 21-day-old nodulated or non-nodulated soybean seedlings, maintained in the absence of nitrogen, were harvested. Proteins and total RNA were isolated from the different plant organs and used for immunoblot and RNA blot analyses, respectively. Protein or RNA blots were separately incubated with antisera or hybridized with probes specific for either ferredoxin-dependent glutamate synthase (Fd-GOGAT) or NADH-dependent glutamate synthase (NADH-GOGAT). The specific activity and the abundance of the Fd-GOGAT peptide and transcript increased, approximately 3–10 times, in cotyledons and hypocotyls/stems in plants germinated in the light compared with those germinated in the dark. Fd-GOGAT activity, peptide, and transcript were highest in leaves. Except for increases in the specific activity of samples from roots treated with (NH4)2SO4 or NH4NO3, there were minor or no changes in Fd-GOGAT activity, peptide and transcript among organs of seedlings treated with different nitrogen sources or by nodulation. Low levels of NADH-GOGAT transcript were detected in all organs. NADH-GOGAT activity, peptide, and transcript increased in roots of seedlings treated with different nitrogen sources, but these changes were more apparent on RNA blots versus immunoblots. The highest NADH-GOGAT activity and most abundant amounts of the peptide and transcript were observed in nodules. Despite being induced by different environmental factors, both GOGAT activities are controlled, at least in part, by either gene expression or by RNA stability, because in most instances, both isoenzymes exhibited paralleled changes in specific activity and the abundance of their corresponding peptides and transcripts on immunoblot and RNA blots, respectively. However, there were some exceptions to the parallel increases in specific activities, peptides and transcripts which suggest that post-translational modification may also regulate the activties of the two GOGAT isoforms. Collectively, the results presented here suggest that the two GOGAT isoforms have distinct physiological functions in soybean.
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  • 4
    Electronic Resource
    Electronic Resource
    Copenhagen : Munksgaard International Publishers
    Physiologia plantarum 104 (1998), S. 0 
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Purified preparations of NAD(H)-glutamate dehydrogenase (GDH, EC 1.4.1.2.) were assayed to determine the effects of mono- and divalent cations, nucleotides and select carbon compounds on NAD(H)-dependent GDH activity. The amination reaction was stimulated 2- to 17-fold by divalent cations (Ca2+ 〉 Cd2+ 〉 Co2+ 〉 Mg2+ 〉 Mn2+ 〉 Zn2+ between 1 and 1000 µM), but the reaction was unaffected by monovalent cations (Na + and K +). The amination reaction was most responsive to changes in Ca2+ in a NADH-dependent manner. The addition of EDTA or EGTA nullified the stimulatory effects of Ca2+. Calmodulin alone or in combination with calmodulin antagonists did not affect the amination reaction. Divalent cations (at 1 mM) inhibited the rate of the deamination reaction by 15 to 25%, while monovalent cations had no effect. ATP inhibited the amination reaction by 10 to 60%, while ADP had little or no effect. ATP or ADP decreased the rate of the deamination reaction 23 to 60 or 20 to 38%, respectively. Many tricarboxylic acid cycle intermediates inhibited the amination reaction, 20 to 50% of the inhibition could be attributed to the chelating capacity of intermediates. Conversely, most of the carbon sources tested did not affect the deamination reaction, the only appreciable differences were increases in activity with sucrose (21%) and glucose (41%) and a decrease in activity with pyruvate (34%). Inhibitors of sulfhydryl groups were used to examine the importance of reduced thiol groups in the amination or deamination reactions. The amination was not dependent on reduced thiol groups, whereas the deamination reaction was dependent on reduced thiol groups.
    Type of Medium: Electronic Resource
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