The pyridine nucleotide cycle in tobacco nicotiana tabacum cultivar samson enzyme activities for the recycling of nad

Wagner, R.; Feth, F.; Wagner, K.G.

Planta (Heidelberg) 167(2): 226-232


ISSN/ISBN: 0032-0935
Accession: 006744822

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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 .fwdarw. NMN .fwdarw. nicotinamide .fwdarw. nicotinic acid .fwdarw. NaMN .fwdarw. nicotinic acid adenine dinucleotide .fwdarw. 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.