Question

Ethylene glycol \(\left(\mathrm{HO}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{OH}\right)\) is a major component of antifreeze. In the body, it is first converted to \(\mathrm{HOOC}-\mathrm{CHO}\) (oxoethanoic acid) and then to \(\mathrm{HOOC}-\mathrm{COOH}\) (oxalic acid), which is toxic. a. What class of enzyme catalyzes the reactions described? b. The treatment for the ingestion of ethylene glycol is an intravenous solution of ethanol. How might this help prevent toxic levels of oxalic acid in the body?

Short answer

a. Oxidoreductase. b. Ethanol competitively inhibits the enzyme alcohol dehydrogenase, reducing the formation of toxic oxalic acid.

Step-by-step solution

Identify the enzyme class for part (a)

First, identify the type of reaction that converts ethylene glycol to oxoethanoic acid and then to oxalic acid. These reactions involve oxidation, indicating that the enzyme involved is an oxidoreductase.

Determine the role of ethanol in part (b)

Ethanol competes with ethylene glycol for the active site of the enzyme alcohol dehydrogenase. By competitively inhibiting this enzyme, ethanol slows down the conversion of ethylene glycol to oxoethanoic acid and subsequently to oxalic acid, thereby reducing the production of toxic oxalic acid in the body.

Key concepts

Oxidoreductase

In the metabolism of ethylene glycol, the initial chemical reactions are catalyzed by a type of enzyme called an oxidoreductase. These enzymes play a key role in oxidation-reduction (redox) processes. During these reactions, one molecule is oxidized (loses electrons) and another is reduced (gains electrons). This kind of enzyme is crucial for the conversion of ethylene glycol into oxoethanoic acid and further into oxalic acid. Understanding oxidoreductase is important because it helps explain why certain treatments, like using ethanol, can be effective in cases of ethylene glycol poisoning. So, in simpler terms, think of oxidoreductases as the enzymes making chemical changes happen by shuffling electrons around.

Competitive Inhibition

The treatment for ethylene glycol poisoning often involves administering ethanol intravenously. This works through a process known as competitive inhibition. In competitive inhibition, a substance (in this case, ethanol) competes with the substrate (ethylene glycol) for the active site on the enzyme.

Here's a quick breakdown:

• The active site of an enzyme is like a lock, and the substrate (what the enzyme acts on) is like a key.
• In competitive inhibition, another 'key' (ethanol) competes for the same lock.
• If the inhibitor (ethanol) binds to the enzyme, it prevents the substrate (ethylene glycol) from entering the active site.

By occupying the active site, ethanol prevents ethylene glycol from being metabolized into toxic oxalic acid. This slows down the harmful process, giving the body more time to filter out ethylene glycol without producing its toxic byproducts.

Alcohol Dehydrogenase

Alcohol dehydrogenase is a specific type of oxidoreductase enzyme that plays a vital role in the metabolism of alcohols in the body, including ethylene glycol. This enzyme helps convert ethylene glycol first into oxoethanoic acid and then further into oxalic acid.

When ethanol is introduced into the body as part of the treatment:

• Ethanol competes with ethylene glycol for binding to alcohol dehydrogenase.
• This competitive inhibition means that fewer molecules of ethylene glycol are metabolized into oxalic acid, reducing its toxicity.
• Thus, alcohol dehydrogenase's role is to metabolize both ethanol and ethylene glycol, but preferentially ethanol when it is present in sufficient amounts.

This competition is beneficial because it mitigates the harmful effects of ethylene glycol by slowing down its conversion into toxic compounds. Hence, understanding the function of alcohol dehydrogenase is essential for comprehending why ethanol works as an antidote in ethylene glycol poisoning.