Lecture 2 Flashcards
What is environmental sensing
Responding to the availability of useful nitrogen containing compounds in the environment
3 reactions
NH3 + Glutamate + ATP -> Glutamine + ADP + Pi
(mediated by glutamine synthetase)
Glutamine + 2-ketoglutarate + NADPH -> 2 glutamate + NADPH
(Uses glutamine synthetase)
NH3 + 2-ketoglutarate + NADPH -> Glutamate + NADP+
(uses glutamate dehydrogenase)
reaction 3 is the most ideal
What does the ammonia assimilatory cycle use
Glutamine synthetase and glutamate synthetase - both needed to get nitrogen inside the cell
What does bacteria do in cases of low NH2 and what do they require
- ammonia assimilatory cycle
- Utilises alternative nitrogen sources
- Fixes N2
All require a change in gene expression
What is nitrogen essential for
For growth and macromolecules to grow and divide
What’s the first level of control of glutamine synthetase activity
Feedback inhibition (products of glutamine metabolism - uses a product of glutamine metabolism. Histidine is a product of this pathway
What’s the second level of control of glutamine synthetase activity
Post translational modification (adenylation).
Each of the 12 subunits (two rings stacked on top of each other) can be adenylated which inactivates each one and enhances susceptibility to the rest of the feedback inhibition.
What’s the third level of control of glutamine synthetase
Controlled at the level of gene expression.
What controls Nrl
Nrl is phosphorylated by Nrll (product of glnl in e.coli.
What is Nrll
A sensor but only has a transmitter domain - it does not sense the environment directly
Ntr control mediation
- Low NH3 -> low glutamine ratio : aketoglutarate ratio
- Utase stimulated
- Utase uridylylates protein PII
- PII interacts with Nrll -> phosophotase
- Nrll -> kinase (autophosphorylates)
- Nrll transfers phosphate to Nrl
- Nrl-P allows open complex formation by s54
