With respect to stereochemistry, what is unique about the reaction catalyzed by aconitase?
a) aconitase can accept substrates of different chiralities, unlike most enzymes.
b) the active site of aconitase alters its stereochemistry upon substrate c) binding.
d) the reaction follows an sn2 mechanism.
e) aconitase converts an achiral molecule into a chiral molecule.

Explanation:

Aconitase is an enzymatic domain. It catalyzes citrate = aconitate + H2O = L-isocitrate. It is important in the aerobic cellular respiration and ATP production. In the catalytic mechanism of mitochondrial aconiatse, there are 2 stages: dehydration and rehydration.  

The activity of aconitase may be reduced if one Fe is removed from cluster and it is also inhibited by nitro-analogs.

Aconitase-catalyzed interconversion of citrate and isocitrate via cis-aconitate: Figure 1

Citrate is prochiral, there is an Hr removed in going to cis-aconitate:

Figure 2

In elimination of water from citrate catalyzed by aconitase there must be anti-elimination to give cis-aconitate.  

Figure 3

The addition reaction of water to cis-aconitate to give citrate (back reaction):

Figure 4

The reaction of addition of water to cis-aconitate to isocitrate. Thus C- is always attacked on the opposite side attack at C-3. Certain studies show that the pro-R proton removed from C-2 of citrate ends up at C-3 of isocitrate:

Figure 4

Overall stereochemistry of the aconitase-catalyzed reaction:

Figure 5

The proton removed from one substrate molecule can be transferred to a different substrate molecule (intermolecular). The OH exchange with solvent, but the proton removed not.

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explanation:

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