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The Entner-Douderoff Pathway

Perhaps because it was the first to be discovered and it fit human biochemistry also, glycolysis of the EMP sort has been so extensively taught even to the exclusion of consideration of other methods. The pathway first outlined by Entner and Douderoff turns out to be by far the most used pathway on earth - by many of the organisms that make up the massive base of the pyramid of life - particularly by all those bacteria grouped as the Pseudomonadaceae. You will soon see how these bacteria annswered the question: "There must be a better way."
Thus any field biologist who is attempting to identify the metabolic types in the soil, and surface waters of the earth should not be stumped by the prevalence of certain intermediates unknown to the EMP.

In the modern world (i.e.: after plants came into existence), glucose is the most common storage compound and thus becomes the food of most recyclers. Glucose, like most other sugars, is actively transported into the cells by the "PTS" (the PhosphoTransferase System in microbes) or by other means. Actually there are several different microbial PTS's, each consisting of several proteins that were each coded by an operon.* These several operons are grouped into several subgroups, each with its own regulators.

These organisms start with ordinary glucose-6-phosphate, and then oxidize it by removing the two H's as shown.

What results is a cyclic ester at the #1 carbon. Cyclic esters are called "lactones." This compound is called gluconolactone. Were it straightened out to the Fischer structure, it would be called gluconic acid (glucose with a carboxyl group for its #1 carbon.

The ring is opened and then the H and OH are removed from carbons #2 and #3 to produce an "enol".

The enol spontaneously has its H on #2 shift to #3 to make the keto-form. You will now note that the top half looks a lot like pyruvic acid. The keto-form splits between carbons #3 and #4: The H on #4's OH shifts to #3, and,

Indeed, pyruvic acid is formed, and the bottom becomes GAP. The things to notice with regards to energetics are:
Only one ATP has been used (to make the G6P).
After only a three or four steps, half of the molecule is already at pyruvate ready for the highly productive Krebs Cycle and attendant ETOP.
Very early NADH's are produced (right after G6P) and those go on to the highly productive ETOP.
Thus a lot of the early, high activation energy steps in glycolysis are circumvented.

* We dwell on microbial PTS systems here because so much metabolic/genetic research involves microbes, and those workers should be aware of these things.

| The Entner-Douderoff Path in brief. |

	In the modern world (i.e.: after plants came into existence), glucose is the most common storage compound and thus becomes the food of most recyclers. Glucose, like most other sugars, is actively transported into the cells by the "PTS" (the PhosphoTransferase System in microbes) or by other means. Actually there are several different microbial PTS's, each consisting of several proteins that were each coded by an operon.* These several operons are grouped into several subgroups, each with its own regulators.

	These organisms start with ordinary glucose-6-phosphate, and then oxidize it by removing the two H's as shown.

	What results is a cyclic ester at the #1 carbon. Cyclic esters are called "lactones." This compound is called gluconolactone. Were it straightened out to the Fischer structure, it would be called gluconic acid (glucose with a carboxyl group for its #1 carbon.

	The ring is opened and then the H and OH are removed from carbons #2 and #3 to produce an "enol".

	The enol spontaneously has its H on #2 shift to #3 to make the keto-form. You will now note that the top half looks a lot like pyruvic acid. The keto-form splits between carbons #3 and #4: The H on #4's OH shifts to #3, and,

	Indeed, pyruvic acid is formed, and the bottom becomes GAP. The things to notice with regards to energetics are: Only one ATP has been used (to make the G6P). After only a three or four steps, half of the molecule is already at pyruvate ready for the highly productive Krebs Cycle and attendant ETOP. Very early NADH's are produced (right after G6P) and those go on to the highly productive ETOP. Thus a lot of the early, high activation energy steps in glycolysis are circumvented.