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Pyruvic Acid

C3H4O3 organic
Molar Mass
88.062 g/mol
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Properties

StateLiquid (colorless to yellowish liquid with acetic acid-like odor)
ColorColorless to yellowish
SolubilityMiscible with water; soluble in ethanol and ether
Melting Point11.8°C
Boiling Point165°C (with decomposition)

About Pyruvic Acid

Pyruvic acid (CH3COCOOH, 88.062 g/mol) is the simplest α-keto acid — a methyl ketone with a carboxyl group on the next carbon. At physiological pH (around 7.4) the carboxyl is fully deprotonated to give pyruvate (pKa = 2.50), which is the form that matters in biochemistry because pyruvate sits at the central branch point of metabolism. Glycolysis converts one glucose into two pyruvate molecules with a net yield of 2 ATP and 2 NADH, and what happens to that pyruvate next defines the difference between aerobic respiration (oxidative decarboxylation by pyruvate dehydrogenase to acetyl-CoA, then citric acid cycle), lactic-acid fermentation (reduction by lactate dehydrogenase to regenerate NAD⁺ in oxygen-starved muscle), alcoholic fermentation (decarboxylation to acetaldehyde and reduction to ethanol in yeast), gluconeogenesis (carboxylation by pyruvate carboxylase to oxaloacetate), and amino acid biosynthesis (transamination to alanine). The pyruvate dehydrogenase complex itself is one of the largest non-ribosomal enzyme assemblies known — roughly 9-10 MDa, with 60 copies each of three enzyme components (E1, E2, E3) wrapped around an icosahedral E2 core, using five different cofactors (TPP, lipoic acid, CoA, FAD, NAD⁺) to hand a substrate from one active site to the next without releasing it.

Where you'll encounter it

If you've ever felt the burn of lactic acid building up in your quadriceps during a hard cycling sprint, your fast-twitch muscle fibers had run pyruvate through lactate dehydrogenase to regenerate NAD⁺ when the mitochondrial respiratory chain couldn't keep up with glycolytic flux. In a brewery or a winery, the same branch point runs the other way — yeast pyruvate decarboxylase strips CO2 off pyruvate to give acetaldehyde, and alcohol dehydrogenase reduces it to ethanol, regenerating NAD⁺ for continued glycolysis. In a dermatology clinic, 40-70% pyruvic acid is the active ingredient in medium-depth chemical peels for acne scars, photodamage, and melasma — the keratolytic and sebostatic action lifts the stratum corneum in controlled depth without the down-time of a TCA peel. And in any biochemistry teaching lab running an enzyme kinetics experiment on lactate dehydrogenase, sodium pyruvate plus NADH plus a UV-Vis cuvette at 340 nm is the standard assay setup — you watch NADH disappear in real time as pyruvate gets reduced to lactate.

Common Uses

  • Substrate for lactate dehydrogenase enzyme kinetics assays at 340 nm UV-Vis
  • Branch-point intermediate teaching example for aerobic respiration vs. fermentation pathways
  • 40-70% chemical peel formulations for acne, photodamage, and melasma in dermatology clinics
  • Pyruvate decarboxylase substrate in yeast bioethanol fermentation and acetaldehyde production
  • Fermentation activity indicator for monitoring microbial metabolism in food and beverage QC
  • Synthetic precursor to L-tryptophan and L-tyrosine via biocatalytic transamination routes

Safety Information

GHS classification: Skin irritation Category 2 (H315), Serious eye irritation Category 2A (H319), Specific target organ toxicity single exposure Category 3 — respiratory (H335). Concentrated pyruvic acid (above 50%) is corrosive to skin and mucous membranes; the 40-70% concentrations used in chemical peels require trained dermatology providers with neutralization protocols ready (sodium bicarbonate solution on hand). OSHA has no specific PEL; ACGIH has not set a TLV. Acute oral LD50 in rats is 2570 mg/kg — moderate toxicity. The decomposition above 165 °C generates acetic acid, CO2, and CO, so heated reactions need vented apparatus. At physiological concentrations (sodium pyruvate IV solutions in clinical research, 1-50 mM in cell culture media) the compound is non-toxic and metabolizes through normal pathways within minutes.

This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.

Constituent Elements

C — Carbon H — Hydrogen O — Oxygen

Frequently Asked Questions

What is the molar mass of pyruvic acid?
88.062 g/mol for the free acid (CH3COCOOH), from 3 × 12.011 (C) + 4 × 1.008 (H) + 3 × 15.999 (O). The sodium salt sodium pyruvate (CH3COCOONa, MW 110.04) is what biochemists usually weigh out for cell culture media and enzyme assays because it's a free-flowing crystalline solid rather than the hygroscopic, decomposition-prone free acid. A 100 mM stock solution is 1.10 g sodium pyruvate per 100 mL of water, sterile-filtered through a 0.22 µm membrane and stored frozen in single-use aliquots.
What happens to pyruvate after glycolysis?
Three main fates depending on oxygen availability and tissue type. Aerobic conditions: pyruvate transports into the mitochondrial matrix via the mitochondrial pyruvate carrier (MPC1/MPC2), gets oxidatively decarboxylated to acetyl-CoA by the pyruvate dehydrogenase complex, and feeds the citric acid cycle for full oxidation yielding about 30 additional ATP per original glucose. Anaerobic muscle: lactate dehydrogenase reduces pyruvate to lactate, regenerating NAD⁺ so glycolysis can keep producing 2 ATP per glucose without waiting for the slower respiratory chain. Yeast and some bacteria: pyruvate decarboxylase strips CO2 to give acetaldehyde, and alcohol dehydrogenase reduces it to ethanol, also regenerating NAD⁺ — the chemistry behind every loaf of bread and every bottle of wine ever made.
Why is the pyruvate dehydrogenase complex so important?
PDC is the irreversible commitment of glucose-derived carbon into oxidative metabolism — once pyruvate becomes acetyl-CoA, the two carbons are headed for CO2 in the citric acid cycle and cannot return to glucose. The complex is enormous (around 9-10 MDa in mammals, comparable in size to a ribosomal subunit), built from 60 copies each of three enzyme components arranged around an icosahedral dihydrolipoyl transacetylase (E2) core. Five cofactors — thiamine pyrophosphate, lipoic acid, coenzyme A, FAD, and NAD⁺ — pass the substrate from active site to active site through the lipoyl swinging arm, never releasing it to bulk solvent. Regulation by reversible phosphorylation of the E1 component (pyruvate dehydrogenase kinase inhibits, pyruvate dehydrogenase phosphatase activates) is the master switch that decides whether glucose is oxidized for energy or diverted to gluconeogenesis, lipogenesis, or amino acid biosynthesis.