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
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