TETROSES: CHARACTERISTICS, ERYTHROSE, SYNTHESIS, DERIVATIVES - BIOLOGY - 2025

The tetroses are monosaccharides four carbons, with the empirical formula C ₄ H ₈ O ₄. There are two types of tetroses: aldoses (they have a terminal aldehyde group, carbon 1 or C-1) and ketoses (they have a ketone group at carbon 2, C-2).

Tetrosses have not been found as natural products, but it is possible to find them in their reduced form, such as erythritol, which is a tetrahydroxyalcohol. In lichens, erythritol is synthesized by decarboxylation of D-arabonic acid.

Source: Ed (Edgar181)

Treoses are not a structural part of living beings. However treoses, such as erythrose, are found in metabolic pathways.

characteristics

In aldotetroses there are two chiral carbon atoms, C-2 and C-3, and carbon 6 (C-6). While in ketotetrose there is only one chiral carbon atom, carbon 3 (C-3).

Sugars, such as tetrose, with the D configuration are more abundant than sugars with the L configuration.

There are two aldotetrose with the D configuration (D-erythrose and D-treose), and one ketotetrose with the D configuration (D-erythrulose).

Fischer projections are made by orienting the molecule in an eclipsed conformation with an aldehyde group above. The four carbon atoms define the main chain of the projection, being arranged vertically. The horizontal links point outward and the vertical links point back.

Unlike monosaccharides that have five or more carbons, which undergo intramolecular reactions to form hemiacetals and hemicetals, tetroses cannot form cyclic structures.

Erythrose in metabolism

Erythrose is the only tetrose found in the metabolism of many organisms. The metabolic pathways in which it is found are:

- Pentose phosphate pathway

- Calvin cycle

- Pathways of biosynthesis of essential and aromatic amino acids.

In all these metabolic pathways, erythrose participates as a phosphate ester, erythrose 4-phosphate. The role of erythrose 4-phosphate in these pathways is described below.

Erythrose in the pentose phosphate pathway and in the Calvin cycle

Both metabolic pathways have in common the biosynthesis of erythrose 4-phosphate with the participation of transketolase and transaldolase enzymes.

Both enzymes catalyze the transfer of a small carbon fragment from a donor ketose to an acceptor aldose to produce a new shorter chain aldose and a longer chain ketosis.

In the pentose phosphate pathway, erythrose-4-phosphate biosynthesis occurs from two substrates, sedoheptulose 7-phosphate, a ketoheptose, and glyceraldehyde 3-phosphate, an aldotriose, which are converted into erythrose 4- phosphate, an aldotetrose, and fructose 6-phosphate, a ketohexose, by catalysis of a transaldolase.

In the Calvin cycle, erythrose-4-phosphate biosynthesis occurs from two substrates, fructose 6-phosphate, a ketohexose, and glyceraldehyde 3-phosphate, as well as an aldotriose. These are converted to erythrose 4-phosphate, an aldotetrose, and xylulose 5-phosphate, a ketopentose, by catalysis of a transketolase.

The biosynthesis of erythrose 4-phosphate in the pentose phosphate pathway is aimed at the biosynthesis of glyceraldehyde 3-phosphate and fructose 6-phosphate, which can continue through the gluconeogenic pathway and the pentose phosphate pathway. The biosynthesis of erythrose 4-phosphate in the Calvin cycle allows the replacement of ribulose 1,5 bisphosphate to restart the cycle with the fixation of CO ₂.

Erythrose: biosynthesis of essential and aromatic amino acids

In bacteria, fungi, and plants, the biosynthesis of the aromatic amino acids phenylalanine, tyrosine, and tryptophan begins with the precursors phosphoenolpyruvate and erythrose 4-phosphate. These precursors are converted first to shikimate and then to chorismate, a seven-step sequence catalyzed by enzymes.

From the corismate there is a bifurcation. On the one hand, one pathway culminates in tryptophan biosynthesis, on the other, chorismate produces tyrosine and phenylalanine.

Because aromatic amino acid biosynthesis only occurs in plants and microorganisms, this pathway is targeted by herbicides, such as glyphosate, which is the active ingredient in RoundUp. The latter is a commercial product of Monsanto, which is currently owned by the Bayer company.

Glyphosate is a competitive inhibitor with respect to phosphoenolpyruvate in the reaction of 5-enolpyruvylshikimate 3-phosphate synthase (EPSP).

Erythritol is a derivative of erythrose

Erythritol is the reduced form of erythrose and shares functional characteristics with other polyols, such as relative stability in acidic and alkaline environments, high heat stability, a taste similar to sucrose (low in calories), not having carcinogenic potential, among other features.

Erythritol is able to suppress harmful bacteria and reduce dental plaque. Unlike other polyols, including sorbitol and xylitol, erythritol is rapidly absorbed from the small intestine, is not metabolized, and is excreted in the urine. Frequent consumption of erythritol reduces the incidence of tooth decay and restores the tooth surface.

Studies on erythritol, xylitol, and sorbitol showed that these sugars differ in their effectiveness against cavities. Xylitol and sorbitol are less effective in preventing tooth decay and periodontal disease.

Prebiotic synthesis of tetroses

The synthesis of monosaccharides in the prebiotic world must have played an essential role in the origin of life since these compounds are sources of energy and components of other biomolecules.

Formaldehyde (CH ₂ = O), the simplest carbohydrate, is among the most abundant of the ~ 140 known interstellar molecules. In the atmosphere of the Primitive Earth, it was generated by the action of ionizing radiation, UV light, and electrical discharges on methane, ammonia and water molecules.

Formaldehyde would have precipitated from the atmosphere, joining hot water currents (60–80 ° C) that would have eroded the earth's rocks, carrying calcium ions.

These ions would have catalyzed a reaction that converts a molecule of formaldehyde and a molecule of protonated formaldehyde (CH ₂ = OH ⁺) into one of protonated glycolaldehyde (HOCH2CH = OH ⁺).

The protonated glycolaldehyde would have interacted with the formaldehyde to produce trioses ⁺, which would have interacted again with the formaldehyde to produce tetroses ⁺. The repetition of this autocatalysis would have produced monosaccharides with a higher carbon number.

The chiralities of tetrosses and other monosaccharides could reflect the chiralities of amino acids present in the aqueous medium, which would also have acted as catalysts for the formation of monosaccharides.

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