Formic Acid
Definition
HCOOH. The toxic terminal metabolite of methanol, produced after alcohol dehydrogenase converts methanol to formaldehyde and aldehyde dehydrogenase oxidises formaldehyde to formate. Causes anion-gap metabolic acidosis and binds to cytochrome c oxidase at the optic nerve, producing blindness.
- Formula
- HCOOH
- Source
- Terminal metabolite of methanol
- Pathway
- Methanol to formaldehyde to formate via ADH and ALDH
- Key toxic effect
- Anion-gap metabolic acidosis, optic nerve injury
Common questions
Why is formic acid considered more dangerous than the methanol that produces it?+
Methanol itself is relatively low in toxicity; the danger lies in its metabolites. Once alcohol dehydrogenase and aldehyde dehydrogenase convert it stepwise to formaldehyde and then formic acid, that formic acid is what actually blocks cellular respiration and drives the acidosis and blindness seen in methanol poisoning.
Why does formic acid specifically bind cytochrome c oxidase rather than other enzymes?+
Formate has a structural and electronic affinity for the copper and heme centres of cytochrome c oxidase, complex IV of the mitochondrial electron transport chain, where it competes with oxygen for the binding site and halts ATP synthesis in oxygen-dependent tissues.
Does ethanol co-ingestion change formic acid production from methanol?+
Yes. Ethanol has a much higher affinity for alcohol dehydrogenase than methanol does, so co-ingested ethanol competitively saturates the enzyme and slows the conversion of methanol into formaldehyde and formic acid, which is the basis of using ethanol as an antidote.
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