Regulation in tobacco callus of enzyme activities of the nicotine pathway

✍ Scribed by R. Wagner; F. Feth; K. G. Wagner

• Publisher: Springer-Verlag
• Year: 1986
• Tongue: English
• Weight: 517 KB
• Volume: 168
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00392369

✦ Synopsis

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 Km value. Such a Km value prevents the complete depletion of the NaMN pool.