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.
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Abbreviations
- HPLC:
-
high-performance liquid chromatography
- NAD-PPase:
-
NAD-pyrophosphatase
- NaMN-ATase:
-
nicotinic-acid mononucleotide (NaMN) adenylyltransferase
- NaMN-GHase:
-
NaMN-glycohydrolase
- Na-PRTase:
-
nicotinic-acid phosphoribosyltransferase
- NMN-ATase:
-
nicotinamide mononucleotide (NMN) adenylyltransferase
- NMN-Ghase:
-
NMN-glycohydrolase
- PMT:
-
putrescine methyltransferase
- Qa-PRTase:
-
quinolinic acid phosphoribosyltransferase
References
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Wagner, R., Feth, F. & Wagner, K.G. Regulation in tobacco callus of enzyme activities of the nicotine pathway. Planta 168, 408–413 (1986). https://doi.org/10.1007/BF00392369
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DOI: https://doi.org/10.1007/BF00392369