Citrate Synthase, CS

Question 1

CS kinetic mech

Answer 1

Ordered sequential mechanism. A must bind to create B’s binding site.

OA = A, must bind to create site for acetyl-CoA = B

Question 2

Structure of CS

Answer 2

dimeric enzyme resembled HK with Open/closed forms… conf select and pop shift.

Open = 2 domains of each SU form deep cleft with OA binding site…
closed = smaller domain rotates and the cleft closes.
this ∆conf will generate acetyl-coA binding site and stop the entrance of water.
This is all conf select and pop shift.

Question 3

What type of rxn occurs here?

Answer 3

mixed aldol-claisen ester condenstion (KNOW THIS so you can give details)
why is this?
aldol = when reacting ketones and aldehydes together by using their a-C attacking the carbonyl of the other guy, this is an aldol rxn.
Claison = esters rcting together (one with a-C attacking a carbonyl)
Ketone with ester = mixed

Question 4

RDS

Answer 4

first step, proton transfer.
why?
bs you are producing an enol, which means you are producing something that requires the removal of proton.
Whenever making something e- deficient, its probably going to be a rate determining step.

Question 5

AA involved

Answer 5

histidine and aspartate.

B+ = histidine (acid)
B: = Aspartate (base)

Question 6

Which proton is being removed in this rxn?

Answer 6

ALPHA proton.

Question 7

Driving force for this rxn

Answer 7

occurs where you are hydrolyzing coA ester…

Question 8

Where does the enol add to?

Answer 8

• adds to a specific face of OA at C = O, need to know its stereospecific because you generated a specific product.

Question 9

When citrate is made…

Answer 9

You make a pro-chiral molecule with a pro-R and a pro-S chain and have added acetyl co-A to make the pro-S arm. This is IMPORTANT!!!! KNOW!!!