Entner–Doudoroff pathway

Entner–Doudoroff pathway is a series of biochemical reactions that metabolize glucose to pyruvate using a route different from glycolysis and the pentose phosphate pathway. It is named after Nathan Entner and Michael Doudoroff, who discovered this pathway in 1952. This pathway is unique because it is primarily found in some bacteria and very rarely in archaea, but not in eukaryotes. It serves as an alternative to glycolysis, allowing organisms that possess it to efficiently utilize glucose under certain conditions.

Overview

The Entner–Doudoroff pathway begins with the conversion of glucose to gluconate-6-phosphate through a two-step process involving the enzymes glucose dehydrogenase and 6-phosphogluconate dehydratase. Gluconate-6-phosphate is then cleaved by KDPG aldolase into pyruvate and glyceraldehyde-3-phosphate. Glyceraldehyde-3-phosphate can enter the glycolytic pathway to be further metabolized to pyruvate, which is a key intermediate in various metabolic processes including the tricarboxylic acid cycle (TCA cycle) and fermentation.

Significance

The Entner–Doudoroff pathway is significant for several reasons. Firstly, it provides a unique metabolic route for the breakdown of glucose, offering an alternative to organisms that lack the full complement of enzymes required for glycolysis or the pentose phosphate pathway. Secondly, it is more energetically efficient under certain conditions, particularly for organisms in environments where the conservation of water is critical, as it consumes less water than glycolysis. Lastly, studying this pathway helps in understanding the diversity of metabolic strategies among different organisms, contributing to our knowledge of evolutionary biology and microbial ecology.

Enzymes Involved

The key enzymes involved in the Entner–Doudoroff pathway include:

• Glucose dehydrogenase: Converts glucose to glucono-δ-lactone, which hydrolyzes spontaneously to gluconate.
• 6-Phosphogluconate dehydratase: Converts 6-phosphogluconate to 2-keto-3-deoxy-6-phosphogluconate (KDPG).
• KDPG aldolase: Cleaves KDPG into pyruvate and glyceraldehyde-3-phosphate.

Pathway Regulation

The regulation of the Entner–Doudoroff pathway is complex and varies among different organisms. It is typically regulated at the genetic level through the induction or repression of enzymes involved in the pathway, depending on the availability of glucose or other sugars. Additionally, the activity of the pathway can be modulated by the energy needs of the cell, with feedback mechanisms in place to balance the production of ATP and NADPH.

Clinical Relevance

While the Entner–Doudoroff pathway is not present in humans, understanding it has implications for medicine and biotechnology. For example, elucidating how pathogenic bacteria utilize this pathway for energy production can aid in the development of new antibiotics. Furthermore, the pathway's enzymes have potential applications in biocatalysis and the biotechnological production of valuable chemicals.

See Also

• Glycolysis
• Pentose phosphate pathway
• Metabolic pathway
• Pyruvate metabolism

• 
  Diagram of the Entner–Doudoroff pathway