aconitase

Question 1

aconitase

Answer 1

• reversible, second enzyme of TCA
  (reversible isomerization)
• with a 180 degree flip of intermediate.

Question 1

citrate

Answer 1

• has a 4 point attachment , binding in such a way that you can do your transformation, and get a single stereoisomer

1. Arg+ salt bridge with pro-S arm
2. His+H bond with OH group
3. Fe in cluster coordinatwe with OH
4. Fe coordinate with COO-

• creates isocitrate from binding with aconitase

Question 2

[4-Fe-4S]

Answer 2

Fe-S clusters used in redox rxns, but this reaction is not a redox, so it is used as a “hook”, which means you are hanging things on it and taking things away.

Iron can change its coordination number (the things its bonded to), can allow us to put things on and take things off.

Question 3

Serine O-

Answer 3

• alkoxide, stabilized by an oxyanion hole. Similar to chymotrypsin, a place that stabilizes your oxyanion
• want to have oxyanion stable so that you can use it
• in this case, you want it to be negative so you can remove pro-R H+ of the Pro-R arm
• this is a proton from an arm that we did NOT JUST MAKE in citrate syntase, that is the pro-S arm.

Question 4

Pro-S arm

Answer 4

coordinated to argenine, which is your pivot point for the 180 flip.
remains salt bridged to COO- of citrate all the way through, does not break.

Question 5

Histidine

Answer 5

ion pairing with something, which allows his to donate a proton in step 1.
In step 2, it will take back the proton….
GA, GB…
The specific proton being taken away is C3, but is redonated to C2, which is following the flip…
CHECK ON THIS REASONING?

Question 6

OH FROM C3

Answer 6

will end up as a water molecule, that is attached to one of the irons in the [4Fe-4S].
This water is involved with a hydrogen bond to the histidine as well.

Question 7

What happens to structure in the cis-aconitate intermediate

Answer 7

you now have a planar system.
C2 and C3 are oriented as such, and this is where the flip occurs.

C2 is now close to the Fe cluster/water molecule and C3 is now close the the serine. (change in orientation)

Arg Likely aids in this process.

Question 8

Why is the intermediate cis?

Answer 8

you have two carboxylates on the same side.

Question 9

Last step of mech

Answer 9

need to ah OH back.
His must be allowed to be fully protonated, which will create a polarized water molecule which will become hydroxide to attack C2, causes electrons to retrieve proton that was originally removed from C3.

REWORK THIS????

Question 10

Things that were added/removed?

Answer 10

• took a proton from C2, added back to C3
• took an OH from C3, added back to C2.

Question 11

Newman projection

Answer 11

sighting down the direction of C2-C3 bond

Question 12

Fluoroacetate

Answer 12

Flourinated acetate… Me groups are now F… When they go through the TCA, you will end up with a F where the pro-R H= would be.
F+ CANNOT be removed, it is the most EN element, which is where certain plants get their toxicity from.