Entner Doudoroff Pathway: overview, diagram, steps, products

Definition Of Entner-Doudoroff Pathway

The Entner-Doudoroff Pathway is an alternative glycolytic pathway found in some bacteria and archaea converting glucose to pyruvate while endowing ATP and NADPH. Unlike the much more common Embden-Meyerhof-Parnas, EMP, pathway (traditional glycolysis), this pathway involves unique enzymatic machinery and intermediates, including 2-keto-3-deoxy-6-phosphogluconate, or KDPG. The ED Pathway is one of the most interesting routes of metabolism in microbial ecology because it shows a very interesting way of producing energy and biosynthesis under certain conditions.

Overview Of The Entner-Doudoroff Pathway

The Entner-Doudoroff Pathway is the process through which glucose is converted into pyruvate and glyceraldehyde-3-phosphate, which are then converted into pyruvate with a resulting production of ATP and NADPH.

Pathway Outline

Overview of Pathway

The following is a step-by-step description of the entire process:

• Phosphorylation of glucose: Glucose becomes phosphorylated by the action of the hexokinase enzyme to result in the product glucose-6-phosphate.

• Cleavage of KDPG: The KDPG aldolase splits KDPG into the products pyruvate and glyceraldehyde-3-phosphate.

• Conversion of G3P: The second G3P is converted in the glycolytic pathway to a second pyruvate, yielding another molecule of ATP.

Comparison With Glycolysis And Pentose Phosphate Pathway

• Energy Yield: In glycolysis, 2 ATP are produced by hydrolysis of each glucose and one in the Entner -Doudoroff pathway. Due to its mainly anabolic nature, the Pentose Phosphate Pathway reduces NADP+.

• Electron Carriers: In place of glycolysis's NADH, Entner-Doudoroff has produced NADPH and NADH. The Pentose Phosphate Pathway, on the other hand, is about getting NADPH.

• Intermediates: The Entner-Doudoroff pathway has specific intermediates, for example, it has KDPG. The intermediates in glycolysis and PPP are present, but there is no specification of the type of compounds. For e.

• Pathway: While Glycolysis is the energetically most productive pathway for a majority of the organisms and the Entner-Doudoroff pathway is used by some bacteria, the PPP is a vital pathway for biosynthesis and redox balance

Detailed Biochemical Steps

The details are given below:

Glucose To 6-Phosphogluconate

Enzymes involved:

• Glucose dehydrogenase

• Gluconolactonase

Reaction mechanism:

• Enzyme: Gluconolactonase

• Mechanism: Gluconolactone is hydrolysed by gluconolactonase to form 6-phosphogluconate.

6-Phosphogluconate to Pyruvate and Glyceraldehyde-3-Phosphate (G3P)

Enzymes Involved:

• 6-Phosphogluconate dehydratase

• KDPG aldolase

Reaction Mechanisms:

• 6-Phosphogluconate to 2-Keto-3-deoxy-6-phosphogluconate (KDPG):

• Enzyme: 6-Phosphogluconate dehydratase

• Mechanism: 6-phosphogluconate is dehydrated by 6-phosphogluconate dehydratase to form KDPG, an intermediate in the pathway.

KDPG to Pyruvate and G3P:

• Enzyme: KDPG aldolase

• Mechanism: KDPG is split by KDPG aldolase to form one molecule of pyruvate and one molecule of glyceraldehyde-3-phosphate (G3P).

Enzymes And Coenzymes Involved

The key enzymes involved are:

Glucose Dehydrogenase:

• Function: It is used to catalyse the reaction where glucose is oxidised.

• Importance: It is important because this enzyme ensures that the pathway does not halt because the compound gluconolactone is not stable.

KDPG Aldolase :

• Function: The enzyme is responsible for cleaving KDPG to pyruvate and glyceraldehyde-3-phosphate (G3P).

• Significance: The enzyme gives the two products emerging on the exit of the pathway and therefore emerging products are available for more metabolism. Most significantly since pyruvate is part of the cycle produced it means the energy demands of the cell and the energy cycle via respiration can be met

The Coenzymes involved are:

NADP+

• Role: Accept electrons from glucose oxidation to gluconolactone

• Function: The reduction of NADP+ to NADPH is the first reaction in this pathway. It represents a very important initial reaction for which adequate reducing power is required for anabolic reactions, for instance, the synthesis of fatty acids and nucleotides.

• Significance: Maintains the balance of reducing and oxidising agents in the cell, and provides reducing equivalents to the biosynthetic pathways.

NAD+

• Role: Although an early coenzyme, NADP↓ is more prominent than NAD+ as a glycolytic coenzyme, because NAD+ could function very well with glycolysis at a more advanced stage of nutrient depletion

• Function: NAD+ is reduced to NADH in glycolysis and all catabolic reactions

Significance: The resulting NADH may be allowed to proceed through the electron transport chain to form ATP and so, in this very important way, links the Entner-Doudoroff pathway to the rest of the cell's catabolic

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