Phosphoketolase (Heterolactic) Pathway

  • The phosphoketolase pathway is distinguished by the key cleavage enzyme, phosphoketolase.
  • Phosphoketolase in the pathway cleaves pentose phosphate into glyceraldehyde-3-phosphate and acetyl phosphate which is the prime reaction of the pathway.
  • As a fermentation pathway, it is employed mainly by the heterolactic acid bacteria which carry out heterolactic fermentation.
  • Heterolactic fermentation is a type of lactic acid fermentation in which sugars (e.g. lactose, glucose) are fermented to a range of acidic products.
  • Examples include some species of Lactobacillus and Leuconostoc.

Steps in Phosphoketolase Pathway

Steps in Phosphoketolase Pathway

  1. Glucose-phosphate is oxidized to 6- phosphogluconic acid.
  2. 6- phosphogluconic acid becomes oxidized and decarboxylated to form pentose phosphate.
  3. Pentose phosphate is subsequently cleaved to glyceraldehyde3- phosphate (GAP) and acetyl phosphate. 
  4. GAP is converted to lactic acid by the same enzymes as the E-M pathway.
  5. The intermediate products formed are 1, 3-diphosphoglyceric acid, 3-phosphoglyceric acid, phosphophenol pyruvic acid, and pyruvic acid.
  6. This branch of the pathway contains oxidation coupled to a reduction while 2 ATP are produced by substrate-level phosphorylation.
  7. Acetyl phosphate is reduced in two steps to ethanol through acetaldehyde, which balances the two oxidations before the cleavage but does not yield ATP.

Overall Reaction

 Glucose ———->1 lactic acid + 1 ethanol +1 CO2 with a net gain of 1 ATP.

The efficiency is about half that of the E-M pathway.

Applications of Phosphoketolase Pathway

  • Heterolactic species of bacteria are occasionally used in the fermentation industry.
  • For example, kefir, a type of fermented milk to yogurt, is produced by is produced using a heterolactic Lactobacillus species which utilize this pathway.
  • Likewise, sauerkraut fermentations use Leuconostoc, a heterolactic bacterium, to complete the fermentation.

Phosphoketolase (Heterolactic) Pathway



About Author

Photo of author

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.

3 thoughts on “Phosphoketolase (Heterolactic) Pathway”

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.