ATCase Flashcards
1
Q
What does ATCase do?
A
- catalyzes an important reaction in biosynthesis
- product is CTP
2
Q
What inhibits ATCase?
A
- CTP inhibits ATCase when end product levels are high
- if there’s a lot of CTP in the cell, there’s no need to make fore
- negative feedback inhbition
- PALA
3
Q
What stimulates ATCase?
A
- ATP
4
Q
Describe the structure for ATCase
A
- multimer with 6 catalytic and 6 regulator subunits
- D3 dihedral symmetry
12 subunits
5
Q
How does ATP affect the binding curve?
A
- ATP shifts curve to the left, less substrate needed to achieve a given v0
- apparent Km decreases
6
Q
How does CTP affect the binding curve?
A
- CTP shifts the binding curve (sigmoidal) to the right
- apparent Km increases
7
Q
What state is favored by CTP binding?
A
- T state (less active)
8
Q
What state is favored by ATP binding?
A
- R state (more active)
9
Q
What does PALA do?
A
- PALA is an ATCase inhibitor (competitive inhibition)
- PALA binds to the catalytic subunits of ATCase
- it looks kind of like a reaction intermediate (bisubstrate analong)
- PALA binds more tightly to the R state, so it technically shifts the equilibrium towards the R state, but it binds tightly to the active sites so it inhibits it
