What is the Difference Between Transketolase and Transaldolase

The main difference between transketolase and transaldolase is that transketolase catalyzes the transfer reaction of a two-carbon ketol group from a ketose sugar to an aldose sugar, while transaldolase catalyzes the transfer reaction of a three-carbon glycolaldehyde unit from a ketose sugar to an aldose sugar.

Transketolase and transaldolase are two enzymes that participate in the pentose phosphate pathway. It is a metabolic pathway that generates NADPH and ribose-5-phosphate for nucleotide synthesis.

Key Areas Covered

1. What is Transketolase 
     – Definition, Features, Catalysis
2. What is Transaldolase
     – Definition, Features, Catalysis
3. Difference Between Transketolase and Transaldolase
     – Comparison of Key Differences

Key Terms

Transketolase, Transaldolase

Difference Between Transketolase and Transaldolase - Comparison Summary

What is Transketolase

Transketolase is a thiamine pyrophosphate-dependent enzyme that catalyzes the transfer of a two-carbon ketol group from a ketose sugar to an aldose sugar. The enzyme has four similar subunits, with each subunit consisting of an N-terminal TPP-binding domain and a C-terminal catalytic domain. The TPP-binding domain is responsible for binding and activating the co-factor TPP, while the catalytic domain contains the active site where the transfer reaction occurs. There are two conserved amino acid residues, His191 and Cys218,  in the active site of transketolase.

Transketolase vs Transaldolase

One function of transketolase is the production of ribose -5-phosphate, which is a precursor for nucleotide synthesis. In the pentose phosphate pathway, transketolase catalyzes the conversion of xylulose -5-phosphate and ribose-5-phosphate to sedoheptulose-7-phosphate  and glyceraldehyde -3-phosphate. Transketolase is also important in the production of NADPH. In the pentose phosphate pathway, transketolase helps to produce NADPH by catalyzing the transfer of a two-carbon unit from a ketose sugar to an aldose sugar and generates NADPH in the process. Transketolase also plays a role in certain disease conditions. In diabetes, the transketolase activity is less, which can lead to the accumulation of harmful metabolic intermediates and the development of complications such as neuropathy and retinopathy. Also, in Alzheimer’s disease too, the transketolase activity is low, which might contribute to the formation of amyloid-beta plaques in the brain.

What is Transaldolase

Transaldosase is an enzyme that is involved in the non-oxidative phase of the pentose phosphate pathway (PPP). Transaldose catalyzes the transfer of a three-carbon dihydroxyacetone moiety from sedoheptulose-7-phosphate to glyceraldehyde -3 – phosphate, resulting in the formation of fructose-6-phosphate and erythrose-4-phosphate. The reaction involves a Schiff base intermediate.

The reaction catalyzed by the transaldolase is reversible. This means that it can also catalyze the reverse reaction in which the fructose-6-phosphate and erythrose-4-phosphate convert back into sedoheptulose-7-phosphate and glyceraldehyde-3-phosphate. Moreover, the concentration of the substrates and the products and the activity of other enzymes in the pathway determine the direction of the reaction.

Compare Transketolase and Transaldolase - What's the difference?

Trasaldolase has been implicated in some diseases, such as cancer, diabetes, and Alzheimer’s disease. In addition, in cancer cells, transaldolase activity is upregulated as a part of the metabolic reprogramming that allows the cancer cells to meet their high biosynthetic demands. Moreover, in diabetes, transaldolase activity is decreased in response to hyperglycemia, while in Alzheimer’s disease, transaldolase activity is decreased in the brain. This contributes to oxidative stress and mitochondrial dysfunction.

Difference Between Transketolase and Transaldolase

Definition

Transketolase is a thiamine pyrophosphate-dependent enzyme that catalyzes the transfer of a two-carbon ketol group from a ketose sugar to an aldose sugar. Transaldosase is an enzyme that is involved in the non-oxidative phase of the pentose phosphate pathway (PPP).

Catalysis

Moreover, transketolase catalyzes the transfer reaction of a two-carbon ketol group from a ketose sugar to an aldose sugar. However, transaldolase catalyzes the transfer reaction of a three-carbon glycolaldehyde unit from a ketose sugar to an aldose sugar.

Substrate Specificity

Transketolase can use either xylulose-5 phosphate or fructose -6- phosphate as the ketose substrate and glyceraldehyde-3 -phosphate or erythrose -4 – phosphate as the aldose substrate while transaldolase is more specific in its substrate requirements. On the other hand, transaldolase uses only sedoheptulose-7-phosphate as the donor of the dihydroxyacetone moiety and glyceraldehyde -3- phosphate as the acceptor.

Conclusion

In brief, transketolase and transaldolase are two enzymes that participate in the pentose phosphate pathway. The main difference between transketolase and transaldolase is that transketolase catalyzes the transfer reaction of a two-carbon ketol group from a ketose sugar to an aldose sugar, while transaldolase catalyzes the transfer reaction of a three-carbon glycolaldehyde unit from a ketose sugar to an aldose sugar.

Reference:

1. “Transaldolase: From biochemistry to human disease.” ScienceDirect.
2. “Transketolase.” ScienceDirect.

Image Courtesy:

1. “Transaldolase Active Site” By Kurtwhite 2009 (CC BY-SA 3.0) via Commons Wikimedia
2. “Transketolase + TPP” By Thomas Shafee – Own work (CC BY-SA 4.0) via Commons Wikimedia

About the Author: Hasini A

Hasini is a graduate of Applied Science with a strong background in forestry, environmental science, chemistry, and management science. She is an amateur photographer with a keen interest in exploring the wonders of nature and science.

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