Nitrogen Fixation and Incorporation Flashcards
What is nitrogen fixation? What is the responsible complex?
Reduction of N2
Eukaryotes can’t do this
Done by nitrogenase complex
Requires lots of energy–8 electrons per N2!
What are the steps of nitrogen fixation?
1) Dinitrogenase reductase transfers electrions from NADH to dinitrogenase
2) Dinitrogenase reduces N2
Very slow rxn–6 molecules per second
What is nitrogen assimilation?
Incorporation of nitrogen into organic molecules
What enzymes make up the nitrogenase complex?
Dinitrogenase and Dinitrogenase reductase
How does nitrogen assimilation work?
1) Glutamine synthetase–catalyzes the reaction:
glutamate + NH4+ -> Glutamine
ATP dependent!
2) Glutamate synthase–reductive amination of alpha-ketoglutarate
Requires NADPH
Doesn’t occur in animals
alpha-ketoglutarate + glutamine + NADPH + H+ -> 2 glutamate + NADP+ + other stuff
What are the two methods of amination of alpha-ketoglutarate?
Direct amination (minor) and reductive amination (major)
What categories of organisms have no “Essential” amino acids?
Plants, prokaryotes
What are the effects of negative nitrogen balance?
Malnutrition–e.g. kwashiorkor
What is the principal source of biosynthetic nitrogen?
Amino acid metabolism
How are nitrogens transported from liver to other proteins?
Branched-chain amino acids
How does the transamination reaction work?
Donor AA + acceptor keto-acid -> new keto acid + new AA
Reversible reaction
What enzymes catalyze transamination reactions?
Transaminases/aminotransferases
Name 3 keto-acid/AA pairs
pyruvate/alanine
glutamate/alpha-ketoglutarate
aspartate/oxaloacetate
What coenzyme is involved in transamination?
PLP (Pyridoxal 5 phosphate)
- form of vitamin B6
- Binds active site
- racemization and decarboxylation reactions
Forms a Schiff base by covalently binding to an enzyme
Imine exchange reaction occurs between PLP and AA
