Tetrose - WikiHQ

In organic chemistry, a tetrose is a monosaccharide with 4 carbon atoms. They have either an aldehyde () functional group in position 1 (aldotetroses) or a ketone () group in position 2 (ketotetroses).

File:DErythrose Fischer.svg | D-Erythrose

File:DThreose Fischer.svg | D-Threose

File:DErythrulose Fischer.svg | D-Erythrulose

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The aldotetroses have two chiral centers (asymmetric carbon atoms) and so 4 different stereoisomers are possible. There are two naturally occurring stereoisomers, the enantiomers of erythrose and threose having the D configuration but not the L enantiomers. The ketotetroses have one chiral center and, therefore, two possible stereoisomers: erythrulose (L- and D-form). Again, only the D enantiomer is naturally occurring.

Biological Functions

There are a few known ways that tetrose sugars are used in nature. Some are seen in metabolic pathways and others are known to affect certain enzymes.

Intermediates in the Pentose Phosphate Pathway

One of the metabolic pathways that a tetrose is involved in is the Pentose Phosphate Pathway. In the Pentose Phosphate Pathway, there is an oxidative stage and a non-oxidative stage. A tetrose sugar, D-erythrose, is utilized in the non-oxidative stage, where D-ribulose 5-phosphate is generated into a 6 carbon sugar (fructose 6-phosphate) and a 3 carbon sugar (glyceraldehyde 3-phosphate). In the Pentose Phosphate Pathway, a transaldolase removes the first 3 carbon molecules of sedoheptulose 7-phosphate and places them onto a glyceraldehyde 3-phosphate. This tetrose diphosphate molecule inhibits the G3P dehydrogenase from performing catalysis because it oxidizes the enzyme by binding to it at the active site. When tetrose diphosphate is bound to the enzyme, the active site of the enzyme is blocked; therefore phosphorolysis of G3P is unable to occur. High concentrations of tetrose diphosphate must be used to outcompete the substrate, G3P, and block the function of G3P dehydrogenase. With the function of glyceraldehyde 3-phosphate dehydrogenase lost, glycolysis cannot proceed. Phosphoglucose isomerase is the second enzyme in the glycolysis pathway, and its role is to convert glucose 6-phosphate into fructose 6-phosphate.