Pyruvate Facts and Oxidation

Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.

Pyruvate (CH₃COCOO − ) is the carboxylate anion or conjugate base of pyruvic acid. It is the simplest of the alpha-keto acids. Pyruvate is a key compound in biochemistry. It is the product of glycolysis, which is the metabolic pathway used to convert glucose into other useful molecules. Pyruvate is also a popular supplement, primarily used to boost weight loss.

Key Takeaways: Pyruvate Definition in Biochemistry

• Pyruvate is conjugate base of pyruvic acid. That is, it is the anion produced when pyruvic acid dissociates in water to form a hydrogen cation and a carboxylate anion.
• In cellular respiration, pyruvate is the end product of glycolysis. It is converted into acetyl coA and then either enters the Krebs cycle (oxygen present), breaks down to yield lactate (oxygen not present), or forms ethanol (plants).
• Pyruvate is available as a nutritional supplement, primarily used to promote weight loss. In liquid form, as pyruvic acid, it is used as a skin peel to reduce wrinkles and discoloration.

Pyruvate Oxidation in Cellular Metabolism

Pyruvate oxidation links glycolysis to the next step of cellular respiration. For each glucose molecule, glycolysis yields a net of two pyruvate molecules. In eukaryotes, pyruvate is oxidized in the matrix of the mitochondria. In prokaryotes, oxidation occurs in the cytoplasm. The oxidation reaction is performed by an enzyme called pyruvate dehydrogenase complex, which is a huge molecule containing over 60 subunits. Oxidation convert the three-carbon pyruvate molecule into a two-carbon acetyl coenzyme A or acetyl CoA molecule. The oxidation also produces one NADH molecule and releases one carbon dioxide (CO₂) molecule. The acetyl CoA molecule enters the citric acid or Krebs cycle, continuing the process of cellular respiration.

The steps of pyruvate oxidation are:

1. A carboxyl group is removed from pyruvate, changing it into a two-carbon molecule, CoA-SH. The other carbon is released in the form of carbon dioxide.
2. The two-carbon molecule is oxidized, while NAD + is reduced to form NADH.
3. An acetyl group is transferred to coenzyme A, forming acetyl CoA. Acetyl CoA is a carrier molecule, which carries the acetyl group into the citric acid cycle.

Since two pyruvate molecules exit glycolysis, two carbon dioxide molecules are released, 2 NADH molecules are generated, and two acetyl CoA molecules continue to the citric acid cycle.

Summary of Biochemical Pathways

While the oxidation or decarboxylation of pyruvate into acetyl CoA is important, it is not the only available biochemical pathway:

• In animals, pyruvate can be reduced by lactate dehydrogenase into lactate. This process is anaerobic, meaning oxygen is not required.
• In plants, bacteria, and some animals, pyruvate is broken down to produce ethanol. This is also an anaerobic process.
• Gluconeogenesis converts pyruvic acid into carbohydrates.
• Acetyl Co-A from glycolysis may be used to produce energy or fatty acids.
• Carboxylation of pyruvate by pyruvate carboxylase produces oxaloacetate.
• Transamination of pyruvate by alanine transaminase produces the amino acid alanine.

Pyruvate as a Supplement

Pyruvate is sold as a weight loss supplement. In 2014, Onakpoya et al. reviewed trials of pyruvate's effectiveness and did find a statistical difference in body weight between people taking pyruvate and those taking a placebo. Pyruvate may act by increasing the rate of fat breakdown. Supplementation side effects include diarrhea, gas, bloating, and increase in low-density lipoprotein (LDL) cholesterol.

Pyruvate is used in liquid form as pyruvic acid as a facial peel. Peeling the skin's outer surface reduces the appearance of fine lines and other signs of aging. Pyruvate is also used to treat high cholesterol, cancer, and cataracts and to boost athletic performance.

Sources

• Fox, Stuart Ira (2018). Human Physiology (15th ed.). McGraw-Hill. ISBN 978-1260092844.
• Hermann, H. P.; Pieske, B.; Schwarzmüller, E.; Keul, J.; Just, H.; Hasenfuss, G. (1999). "Haemodynamic effects of intracoronary pyruvate in patients with congestive heart failure: an open study." Lancet. 353 (9161): 1321–1323. doi:10.1016/s0140-6736(98)06423-x
• Lehninger, Albert L.; Nelson, David L.; Cox, Michael M. (2008). Principles of Biochemistry (5th ed.). New York, NY: W. H. Freeman and Company. ISBN 978-0-7167-7108-1.
• Onakpoya, I.; Hunt, K.; Wider, B.; Ernst, E. (2014). "Pyruvate supplementation for weight loss: a systematic review and meta-analysis of randomized clinical trials." Crit. Rev. Food Sci. Nutr. 54 (1): 17–23. doi:10.1080/10408398.2011.565890
• The Royal Society of Chemistry (2014). Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book). Cambridge: p. 748. doi:10.1039/9781849733069-FP001. ISBN 978-0-85404-182-4.