What enzyme does fluoroacetate inhibit?
Fluoroacetate (FA; CH2FCOOR) is highly toxic towards humans and other mammals through inhibition of the enzyme aconitase in the tricarboxylic acid cycle, caused by ‘lethal synthesis’ of an isomer of fluorocitrate (FC).
What happens if aconitase is inhibited?
Aconitase is inhibited by fluoroacetate, therefore fluoroacetate is poisonous. Fluoroacetate, in the citric acid cycle, can innocently enter as fluorocitrate. However, aconitase cannot bind this substrate and thus the citric acid cycle is halted.
Why does Fluorocitrate inhibit aconitase?
Fluorocitrate is converted to fluoro-cis-aconitate and then to 4-hydroxy-trans-aconitate (HTn) which binds tightly to aconitase and inhibits its action. It does this by displacing the double bond closest to the Fe and preventing the hydration of the double bond.
What role does the aconitase iron sulfur cluster play in aconitase catalysis?
Aconitase contains a 4Fe-4S iron-sulfur cluster. This iron sulfur cluster does not participate in redox as most do, but holds the OH group of citrate to facilitate its elimination. It is at this 4Fe-4S site that catalysis occurs and citrate or isocitrate is bound.
Does fluoroacetate inhibit citrate synthase?
Sodium Fluoroacetate This inhibits the enzyme aconitase, which inhibits conversion of citrate to cis-aconitic acid/isocitrate. This inhibition will lead to a buildup of citric acid resulting in convulsions and death from cardiac failure or respiratory arrest. Mitochondrial uptake of acetate may also be affected.
How does fluoroacetate inhibit TCA cycle?
Fluoroacetate combines with coenzyme A (CoA-SH) to form fluoroacetyl CoA, which can substitute for acetyl CoA in the tricarboxylic acid cycle and reacts with citrate synthase to produce fluorocitrate, a metabolite of which then binds very tightly to aconitase, thereby halting the cycle.
Why is aconitase important?
Aconitase plays a significant role in the tricarboxylic acid cycle portion of cellular respiration (aka TCA, Krebs cycle, or citric acid cycle). Aerobic organisms use this cycle to oxidize acetyl-coA into carbon dioxide and generate energy in the form of ATP, NADH, and FAHD2 (Figure 1).
What does aconitase do in the citric acid cycle?
Mitochondrial aconitase converts citrate to isocitrate in the tricarboxylic acid cycle (TCA) and serves as a TCA cycle regulatory enzyme sensitive to oxidation.
Which step in the TCA cycle is inhibited by fluoroacetate?
Fluoroacetate produces its toxic action (after conversion to fluorocitrate) by inhibiting the Krebs cycle. The compound is incorporated into fluoroacetyl coenzyme A, which condenses with oxaloacetate to form fluorocitrate.
Is fluorocitrate toxic?
The classical explanation of the toxic action of fluorocitrate is that it inhibits the enzyme aconitase in the tricarboxylic acid cycle. Deactivation of aconitase results in decreased energy production by cells and ultimately death of the organism.
What happens when the protein aconitase binds to iron?
The iron-responsive element binding protein/cytosolic aconitase functions as either an RNA binding protein that regulates the uptake, sequestration, and utilization of iron or an enzyme that interconverts citrate and isocitrate. These mutually exclusive functions are regulated by changes in cellular iron levels.
How is aconitase regulated?
Aconitase (top) and the same protein acting as an iron regulatory protein bound to part of a messenger RNA. Aconitase is an essential enzyme in the citric acid cycle and iron regulatory protein 1 interacts with messenger RNA to control the levels of iron inside cells.
What is the mechanism of the inhibitory effect of FA on aconitase?
The mechanism of the inhibitory effect of FA on aconitase (citrate (isocitrate) hydro-lyase, EC 22.214.171.124) is one of the most interesting in biochemistry. Upon entering an organism, nontoxic FA undergoes a series of metabolic conversions, the result of which is synthesis of highly toxic FC; this process was termed lethal synthesis ( Peters, 1952 ).
What is the action of fluoroacetate?
Action of fluoroacetate (FA) becomes apparent after a latent period, even after exposure to lethal doses. The best-known representative of FA is its sodium salt. There are also series of fluorinated compounds whose metabolism is connected with the formation of FA.
How does aconitase affect the conversion of citrate to isocitrate?
Aconitase affects the conversion of citrate to isocitrate through an intermediate, cis -aconitate, which binds with aconitase in two different ways, swung 180° to the C α −C β bond ( Gawron and Mahajan, 1966 ).
How does peroxynitrite react with C-aconitase?
Peroxynitrite also reacts with the Fe-S cluster of c-aconitase in different cell culture types, promoting total cluster disruption with the consequent enzyme inactivation, but turning on its iron-responsive activity ( Castro et al., 1998; Soum et al., 2003 ).