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NITROGEN METABOLISM

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animals

plants

fungi

Nitrogen is essentialfor all organisms(in amino acids andnucleic acids).

Most of the conversionsbetween organic and inorganicnitrogen are catalyzedby bacterial and archaeal enzymes.

oxidative reductive

Nitrogen fixation

Reduced nitrogen (amines, amides) is required for proteins, nucleic acids, et al. Environmental supplies of nitrogen are oxidized (N2,

NO3-) Issues include N fixation (prokaryotes only) N2 + 16 ATP + 10 H+ + 8 e- Nitrogenase reductase, nitrogenase

2 NH4+ + H2 + 16 ADP + 16 Pi and nitrate reduction (bacteria, plants, fungi)

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Nitrate reductase, nitrite reductase

In bacteria, the electron donor is NADPH

+5 +3

+3 -3

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Ammonium assimilation glutamate dehydrogenase

NADPH NADP+

-KG glu NH4+ H2O

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Ammonium assimilation

Glutamine synthetase GOGAT (glutamine oxo-glutarate amino transferase)

ATP NH4+ ADP + Pi GS glu gln NAD+ NADH or Fd(ox) Fd(red) GOGAT glu -KG

Glutamate and glutamine are major –NH2 donors through transaminases e.g., Glu +OAA -KG + Asp

Glutamate and glutamine are major –NH2 donors through transaminases e.g., Glu +OAA -KG + Asp

Urea cycle: removal of excess N

Pre-urea cycle: formation of carbamyl phosphate

Urea cycle:

Lose two amino-Nand a CO2

Follow the N fromcarbamoyl-P(green arrow) andthe N from aspartate(red arrow).

How much energydoes it take to remove two amino-nitrogens?

How many of the reactions that we have studied are represented in excretion of excess nitrogen?

Summary

•Nitrogen enters the biosphere through plants, fungi, but mainly bacteria and archaea

•Plants, fungi, and bacteria reduce nitrate nitrogen to ammonium •Ammonium is incorporated into organic molecules by glutamate

dehydrogenase and glutamine synthase/GOGAT•Other amino acids are formed by transamination•The urea cycle removes nitrogen from ammonia and alanine

as urea