Uronic Acid Pathway

  • Uronic acids are a class of sugar acids with both carbonyl and carboxylic acid functional groups.
  • They are sugars in which the terminal carbon’s hydroxyl group has been oxidized to a carboxylic acid.
  • Oxidation of the terminal aldehyde instead yields an aldonic acid, while oxidation of both the terminal hydroxyl group and the aldehyde yields an aldaric acid.
  • The names of uronic acids are generally based on their parent sugars, for example, the uronic acid analog of glucose is glucuronic acid.
  • Uronic acids derived from hexoses are known as hexuronic acids and uronic acids derived from pentoses are known as penturonic acids.


The glucuronic acid pathway is a quantitatively minor route of glucose metabolism. Like the pentose phosphate pathway, it provides biosynthetic precursors and inter-converts some less common sugars to ones that can be metabolized. 


  • Uronic acid pathway is an alternative oxidative pathway for glucose metabolism.
  • It catalyzes the conversion of glucose to glucuronic acid, ascorbic acid, and pentoses.
  • It does not lead to the formation of ATP.


  • In cytoplasm of the cell
  • Tissue distribution: Liver and Adipose tissue

Steps of Uronic Acid Pathway

Steps of Uronic Acid Pathway

  • STEP 1: Glucose 6-phosphate is converted to Glucose1-phosphate via phosphoglucomutase.
  • STEP 2: Glucose 1-phosphate reacts with uridinetriphosphate (UTP) via UDP glucosepyrophosphorylase to form UDP glucose.
  • STEP 3: UDP glucose is oxidized at C6 by a 2-step process via an NAD +-dependent UDP glucosedehydrogenase  to form UDP glucuronic acid.
  • STEP 4: UDP glucuronic acid is hydrolysed to form UDP and D-glucuronic acid.


  • Source of glucuronate for reactions involving its incorporation into proteoglycans.
  • conjugated to nonpolar acceptor molecules such as steroid hormones, some drugs, bilirubin, or other foreign compounds in the liver for easier excretion via the bile.
  • STEP 5: Oxidation of D-glucuronic acid to L-gulonic acid via L- gulonic dehydrogenase   in the presence of NADPH2.


  • It is the direct precursor of ascorbate in those animals capable of synthesizing this vitamin, in an NADPH-dependent reaction.
  • In humans, ascorbic acid cannot be synthesized because of the absence of L-gulonolactone oxidase.
  • STEP 6: Oxidation of L-Udonic acid
    • L-gulonic acid may be oxidized to 3-keto-L-gulonicacid via β -L-hydroxy acid dehydrogenase.
    • NADH is generated.
  • STEP 7: Decarboxylation of 3-Keto-L-Gulonic Acid
    • Followed by decarboxylation of 3-keto-L-gulonicacid to form L-xylulose,a ketopentose via β-L- gulonate decarboxylase ; here, carbon 1 of 3-keto-L-gulonic acid is released as CO2. 
  • STEP 8: Oxidation of L-Xylulose
    • L-xylulose is then reduced to xylitol via xylitoldehydrogenase  (or xylulosereductase)
  • STEP 9: Reoxidation of Xylitol
  • STEP 10: Phosphorylation of D-Xylulose
    • D-xylulose is phosphorylated at carbon 5 to form D-xylulose 5-phosphat via xylulose kinase 
    • Further metabolized via the HMP Shunt
    • Converted to intermediates of glycolysis for energy production

Regulation of Uronic Pathway

  • Administration of drugs i.e. Chlorobutanol & Barbital significantly increases the uronic acid pathway.
  • Certain drugs are also found to enhance the synthesis of Ascorbic acid.

Significance of Uronic Pathway

  • It is an alternative oxidative pathway for glucose.
  • It is concerned with the synthesis of glucuronic acid, pentoses & vitamin-ascorbic acid (except in primates & guinea pigs).
  • Major function is to produce D-Glucuronic acid which is required for: Detoxification of foreign chemicals and synthesis of mucopolysaccharides.
  • Many wastes in the human body are excreted in the urine as their glucuronate salts,
  • Iduronic acid is a component of some structural complexes such as proteoglycans.


  1. Rodwell, V. W., Botham, K. M., Kennelly, P. J., Weil, P. A., & Bender, D. A. (2015).  Harper’s illustrated biochemistry (30th ed.). New York, N.Y.: McGraw-Hill Education LLC.
  2. John W. Pelley, Edward F. Goljan (2011). Biochemistry. Third edition. Philadelphia: USA.
  3. https://www.scribd.com/document/328465491/2-4-Biochemistry-Tca-Hmp-and-Uronic-Acid-Pathway
  4. https://www.slideshare.net/sathi3366/presentation-29571791.

About Author

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Sagar Aryal

Sagar Aryal is a microbiologist and a scientific blogger. He attended St. Xavier’s College, Maitighar, Kathmandu, Nepal, to complete his Master of Science in Microbiology. He worked as a Lecturer at St. Xavier’s College, Maitighar, Kathmandu, Nepal, from Feb 2015 to June 2019. After teaching microbiology for more than four years, he joined the Central Department of Microbiology, Tribhuvan University, to pursue his Ph.D. in collaboration with Helmholtz-Institute for Pharmaceutical Research Saarland (HIPS), Saarbrucken, Germany. He is interested in research on actinobacteria, myxobacteria, and natural products. He has published more than 15 research articles and book chapters in international journals and well-renowned publishers.

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