Qu i c k T i m e ™ a n d a
T I F F (U n c o m p re s s e d ) d e c o m p re s s o r
a re n e e d e d to s e e th i s p i c t u re .
NITROGEN METABOLISM
Nitrogen is essential
for all organisms
(in amino acids and
nucleic acids).
oxidative
Most of the conversions
between organic
and inorganic
nitrogen are catalyzed
by bacterial and
archaeal enzymes.
reductive
Qu i c k T i m e ™ a n d a
T I F F (U n c o m p re s s e d ) d e c o m p re s s o r
a re n e e d e d to s e e th i s p i c t u re .
plants
animals
fungi
Nitrogen fixation
Reduced nitrogen (amines, amides) is required for
proteins, nucleic acids, et al.
Environmental supplies of nitrogen are oxidized (N2,
NO3-)
Iss ues include N fixation (prokaryotes only)
N2 + 16 ATP + 10 H+ + 8 eNitrogenase reductase, nitrogenase
2 NH 4+ + H 2 + 16 ADP + 16 Pi
and nitrate reduction (bacteria, plants, fun gi)
Qu i c k T i m e ™ a n d a
T I F F (U n c o m p re s s e d ) d e c o m p re s s o r
a re n e e d e d to s e e th i s p i c t u re .
Nitrat e reductas e, nitrite reductase
+5
+3
+3
-3
Qu i c k T i m e ™ a n d a
T I F F (U n c o m p re s s e d ) d e c o m p re s s o r
a re n e e d e d to s e e th i s p i c t u re .
In bacteria, the electron donor is NADP H
Ammonium assimilation
gluta mate dehydrogenase
Qu i c k T i m e ™ a n d a
T I F F (U n c o m p re s s e d ) d e c o m p re s s o r
a re n e e d e d to s e e th i s p i c t u re .
Ammonium assi milation
Gluta mine synth etase
GOGAT
(glutamine oxo-glutarate amino transferase)
Urea cycle: removal of excess N
Pre-urea cycle: formation of carbamyl phosphate
Urea cycle:
Lose two amino-N
and a CO2
Follow the N from
carbamoyl-P
(green arrow) and
the N from aspartate
(red arrow).
How much energy
does 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