Question

The TCA cycle in a particular tissue has been inhibited by fluoroacetate. However, it is not the fluoroacetate that is responsible for the inhibition. It gets converted to another molecule that enters the TCA cycle and is transformed into the inhibitor.
a. Propose the inhibitor molecule and mechanistically show the conversion of fluoroacetate to the inhibitor.
b. Indicate at what step fluoroacetate ultimately inhibits the TCA cycle.
c. Explain why you think fluoroacetate acts as an inhibitor of this enzyme? Your answer should include some sort of mechanistic explanation.
d. What difference in the concentration of each TCA cycle metabolite would you expect, compared with a normal uninhibited tissue? List each metabolite and indicate the effect on its concentration.

Answer 1

Answer:

TCA cycle in particular is inhibited by fluoroacetate. Fluoroacetate is a compound the binds to the Coenzyme A of the Krebs cycle to form Floroacetyl CoA which in turn forms fluorocitrate instead of forming citrate. This fluorocitrate is not able to bind to aconitase enzyme preventing the conversion in to isocitrate, thereby halting the Krebs cycle.

a) The inhibitor molecule here is Fluorocitrate.

t a Coa-sa Co ASH Coenzyme A Fro Nat Fluoroacetate Fluoroacetyl COA Citrate Hooc-ch-F Hooc-c-one Hooc-ch, Fluoro citrate

b) see attachment below

c) The fluoroacetate along with Coenzyme A forms Fluoroacetyl CoA which in turn forms Fluorocitrate in place of citrate formation. Fluorocitrate does not bind to Aconitase hance isocitrate is not formed and the Krebs cycle in halted.

See attached file for the continuation of c.

The above mechanism shows the inhibition of aconitase, where the presence of fluorine causes resonance to occur after the flip step preventing the Ser 642 moiety of Aconitase from binding and no isocitrate conversion.

d) As compared to the normal tissues the, due to the inhibition of aconitase enzyme, the citrate isocitrate conversion will proceed at a very slow rate thereby halting TCA cycle and the concentrations of the further produced components:

Citrate concentration increased

Isocitrate concentration reduced

Alpha - ketoglutarate concentratioin reduced

Succinyl CoA concentration reduced

Succinate concentration reduced

Fumarate concentration reduced

Malate concentration reduced

Oxaloacetate concentration reduced