Alpha-ketoglutarate, a key molecule involved in nitrogen circulation in both animals and plants, in the context of human gut microbiota and protein metabolism

• Purpose: Nitrogen (N2) is an indispensable metabolite required for the synthesis of protein. In animals, gut bacteria and, to a certain extent, even hepatocytes, are able to assimilate nitrogen from ammonium (NH4+), which is essentially derived from the amine group (-NH2) and which is at the same time a very toxic metabolite. Initially, NH4+ is coupled to alpha-ketoglutarate (AKG), a reaction which results in the appearance of glutamate (one amine group), and after that, in the appearance of glutamine - containing two amine groups. The surplus of NH4+ which is not utilized by AKG/glutamate/glutamine is eliminated as urea in the urine, via the urea cycle in hepatocytes. Plants bacteria also assimilate nitrogen from NH4+, by its fixation to ammonia (NH3)/NH4+. Materials/methods: Previous studies have shown that AKG (also known as 2-oxo-glutaric acid or 2-oxopentanedioic acid), the primary metabolite of Rhizobium and gut bacteria, is essential for the assimilation of nitrogen. Results: Symbiotic bacteria produce AKG, which together with glutamate dehydrogenase (GDH), ‘generates’ primarily amine groups from NH4+. The final product is glutamate – the first amino acid. Glutamate has the capacity to be converted to glutamine, through the action of glutamine synthetase, after the assimilation of the second nitrogen from NH4+. Conclusion: Glutamate/glutamine, derivatives of AKG metabolism, are capable of donating amine groups for the creation of other amino acids, following NH2 transamination to certain metabolites e.g., short chain fatty acids (SCFA).

Subject headings

NATURVETENSKAP  -- Biologi -- Zoologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Zoology (hsv//eng)

Keyword

Amino acids

E. coli

Gastrointestinal tract

Nitrogen fixation

Rhizobium

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