Nitrogen recycling during phenylpropanoid metabolism in sweet potato tubers.
In the first step of the phenylpropanoid metabolic pathway, L-phenylalanine (L-Phe) is deaminated to form E-cinnamate, in a conversion catalyzed by phenylalanine ammonia-lyase (PAL; EC 4.3.1.5). The metabolic fate of the ammonium ion (NH4+) produced in this reaction was investigated in sweet potato (Ipomoea batatas) tuber discs. [15N]-Labeled substrates including L-Phe, in the presence or absence of specific enzyme inhibitors, were administered to sweet potato discs in light under aseptic conditions. 15N-Nuclear magnetic resonance spectroscopic analyses revealed that the 15NH4+ liberated during the PAL reaction is first incorporated into the amide nitrogen of L-glutamine (L-Gln) and then into L-glutamate (L-Glu). These results extend our previous observations in pine and potato that PAL-generated NH4+ is assimilated by the glutamine synthetase (GS; EC 6.3.1.2)/glutamate synthase (GOGAT; EC 1.4.1.13) pathway, with the NH4+ so formed ultimately being recycled back to L-Phe via L-Glu as aminoreceptor and donor.
Singh
S
S
Department of Botany, University of British Columbia, Vancouver,  Canada.
Lewis
N G
NG
Towers
G H
GH
D000643:Ammonium Chloride / Q000737:chemistry; D003624:Darkness; D004791:Enzyme Inhibitors; D008401:Gas Chromatography-Mass Spectrometry; D018698:Glutamic Acid / Q000737:chemistry; D005973:Glutamine / Q000737:chemistry; D007189:Indans / Q000737:chemistry; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D009584:Nitrogen / Q000737:chemistry / Q000378:metabolism*; D009587:Nitrogen Isotopes; D010649:Phenylalanine / Q000378:metabolism*; D010650:Phenylalanine Ammonia-Lyase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D018547:Plant Stems / Q000378:metabolism*; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D019657:Solanaceae / Q000378:metabolism; D013997:Time Factors; D014443:Tyrosine / Q000378:metabolism
D004791:Enzyme Inhibitors; D007189:Indans; D009587:Nitrogen Isotopes; D000644:Quaternary Ammonium Compounds; D000643:Ammonium Chloride; D005973:Glutamine; D018698:Glutamic Acid; D014443:Tyrosine; D010649:Phenylalanine; D010650:Phenylalanine Ammonia-Lyase; D009584:Nitrogen