Nitrogen recycling in phenylpropanoid metabolism

Abstract

Approximately 30-45% of plant organic matter is derived from L-phenylalanine, and to a lesser extent from L-tyrosine, through the cinnamate pathway. In the initial step, mediated by phenylalanine ammonia lyase, cinnamic acid and an equimolar amount of ammonium ion is generated. To determine the metabolic fate of the ammonia formed, [15N]-L-phenylalanine was administered to potato discs in the light under aseptic conditions. It was found, using 15N NMR spectroscopic analyses, that this nitrogen is first incorporated into the amide nitrogen of glutamine and then into glutamate. When incubations were repeated in the presence of methionine-S-sulphoximine, a known inhibitor of glutamine synthetase, only resonances corresponding to 15NH4+ and [15N]-L-Phe accumulated. It is proposed that during active phenylpropanoid metabolism, the ammonia released by phenylalanine ammonia lyase/tyrosine ammonia lyase is efficiently recycled back to Phe/Tyr with glutamate serving as aminoreceptor and donor. This is the first evidence for a novel nitrogen cycle in plants.

Source or Periodical Title

Phytochemistry

ISSN

319422

Page

31-35

Document Type

Article

Subject

15 N NMR spectroscopy, Amino acids, L-glutamine, L-phenylalanine, Nitrogen (ammonia) recycling, Phenylpropanoid biosynthesis, Solanaceae, Solarium tuberosum

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