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The Entner-Douderoff Pathway

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). Actually there are several different 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.

	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). Actually there are several different 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.