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  • 1
    Electronic Resource
    Electronic Resource
    The pyridine-nucleotide cycle in tobacco (1986)
    Springer
    Planta 167 (1986), S. 226-232 
    Details
    ISSN: 1432-2048
    Keywords: NAD pyrophosphatase ; Nicotinamidase ; Nicotiana (pyridine-nucleotide cycle) ; Nicotine biosynthesis ; Pyridine nucleotide cycle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In order to elucidate the NAD-recycling pathway the following enzyme activities have been characterized in different tobacco tissues and in tomato root: NAD pyrophosphatase, nicotinamide mononucleotide (NMN)/nicotinic acid mononucleotide (NaMN) glycohydrolases, nicotinamidase and nicotinic acid phosphoribosyltransferase. The investigations were performed with protein extracts purified by gel filtration and enzymatic activities were determined by high-performance liquid chromatography methods. The kinetic parameters of the different enzymes from tobacco root and their specificity are reported. The data are in favor of the so-called pyridine-nucleotide cycle VI (NAD→NMN→nicotinamide→nicotinic acid→NaMN→nicotinic acid adenine dinucleotide→NAD). In the nicotine-producing tobacco root a further direct route leading from NaMN to nicotinic acid is proposed. These data are reconciled with the assumption that it is nicotinic acid which is provided by the pyridine-nucleotide cycle for the synthesis of nicotine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391419
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Regulation in tobacco callus of enzyme activities of the nicotine pathway (1986)
    Springer
    Planta 168 (1986), S. 402-407 
    Details
    ISSN: 1432-2048
    Keywords: Methylputrescine oxidase ; Nicotiana ; Nicotine biosynthesis ; Ornithine decarboxylase ; Putrescine methyltransferase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Nicotine synthesis was stimulated by reduction of the medium auxin concentration (induction medium) in callus tissue originating from Nicotiana tabacum cv. Samsun. The enzyme activities of the route ornithine to methylpyrroline, which are those of ornithine decarboxylase, putrescine methyltransferase and methylputrescine oxidase, were determined during callus growth in the induction medium and as a control under non-nicotine-stimulating conditions (growth medium). The enzymes were assayed by high-performance liquid chromatography. Whereas the activities of ornithine decarboxylase were very similar under nicotine-stimulating and non-stimulating conditions, those of putrescine methyltransferase and methyl-putrescine oxidase increased strongly in the induction medium. In addition, the pools of putrescine and methylputrescine were determined throughout the callus growth cycle. Both sets of data strongly confirm the supposition that putrescine methyl-transferase is the enzyme under stringent control for nicotine biosynthesis, whereas the subsequent methylputrescine oxidase is co-regulated, although less stringently.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392368
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
    Fulltext
  • 3
    Electronic Resource
    Electronic Resource
    Regulation in tobacco callus of enzyme activities of the nicotine pathway (1986)
    Springer
    Planta 168 (1986), S. 408-413 
    Details
    ISSN: 1432-2048
    Keywords: Callus culture (nicotine pathway) ; Nicotiana (nicotine pathway) ; Nicotine biosynthesis ; Pyridine nucleotide cycle ; Pyridine nucleotide glycohydrolase ; Quinolinic acid phosphoribosyltransferase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In tobacco callus, the induction of nicotine synthesis, which stimulates enzyme activities of the ornithine-methylpyrroline route (see the preceding paper), also leads to marked changes in the enzyme activities of the pyridine-nucleotide cycle. This cycle provides the metabolite (probably nicotinic acid) for condensation with methylpyrroline to produce nicotine. The activities of eight enzymes of the pyridine-nucleotide cycle and of quinolinic-acid phosphoribosyltransferase, the anaplerotic enzyme, were determined by high-performance liquid chromatography assays. The distinct changes of their activities upon induction of nicotine synthesis lead to the following conclusions: i) nicotinic acid is the relevant metabolite which is provided by the pyridine-nucleotide cycle and consumed for nicotine synthesis. ii) The enhancement of the nicotinic-acid pool arises in two ways, by synthesis of NAD and degradation via nicotinamide mononucleotide and by a direct route from nicotinic-acid mononucleotide (NaMN) which is degraded by a glycohydrolase with a rather high K m value. Such a K m value prevents the complete depletion of the NaMN pool.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00392369
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
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