The key difference between transaldolase and transketolase is their function. Transaldolase catalyzes the conversion of sedoheptulose 7-phosphate and glyceraldehydes 3-phosphate into erythrose 4-phosphate and fructose 6-phosphate, while transketolase catalyzes the conversion of xylulose 5-phosphate and ribose 5-phosphate into glyceraldehyde 3-phosphate and sedoheptulose 7-phosphate.
The pentose-phosphate pathway is a metabolic pathway that takes place parallel to glycolysis. It consists of two distinct pathways. In the pentose phosphate pathway, NADPH is generated in the oxidative phase, while pentose sugars are generated in the non-oxidative phase. In addition to pentoses and NADPH, this pathway generates ribose 5-phosphate, which is a precursor for nucleotide synthesis. Transaldolase and transketolase are two enzymes involved in the non-oxidative phase of the pentose phosphate pathway.
CONTENTS
1. Overview and Key Difference
2. What is Transaldolase
3. What is Transketolase
4. Similarities Between Transaldolase and Transketolase
5. Side by Side Comparison – Transaldolase vs Transketolase in Tabular Form
6. Summary
What is Transaldolase?
Transaldolase is an enzyme catalyzing the conversion of sedoheptulose-7-phosphate and glyceraldehyde-3-phosphate into erythrose-4-phosphate and fructose-6-phosphate. Hence, it participates in the non-oxidative phase of the pentose phosphate pathway. Transaldolase, together with transketolase, links the pentose phosphate pathway and glycolysis with each other.
Figure 01: Transaldolase
Structurally, it is an enzyme about 34kDa, and it has a single domain of 337 amino acids. It is found almost ubiquitously in archaea, bacteria and eukarya. The gene TALDO1 codes for this enzyme in humans.
What is Transketolase?
Transketolase is another enzyme involved in the non-oxidative phase of the pentose phosphate pathway. This enzyme is found in a wide range of organisms, including bacteria, plants, and mammals. It catalyzes the conversion of xylulose 5-phosphate and ribose 5-phosphate into glyceraldehyde 3-phosphate and sedoheptulose 7-phosphate.
Figure 02: Transketolase
Moreover, it catalyzes the conversion of xylulose 5-phosphate and erythrose 4-phosphate into glyceraldehyde 3-phosphate and fructose 6-phosphate. The gene TKT codes for the enzyme transketolase. Similar to transaldolase, transketolase facilitates the link between glycolysis and the pentose phosphate pathway.
What are the Similarities Between Transaldolase and Transketolase?
- Both transaldolase and transketolase are enzymes participating in the pentose phosphate pathway.
- They catalyze the reactions of the non-oxidative phase of PPT.
- Transaldolase and transketolase link glycolysis and pentose phosphate pathway.
What is the Difference Between Transaldolase and Transketolase?
Transaldolase is an enzyme catalyzing the conversion of sedoheptulose 7-phosphate and glyceraldehydes 3-phosphate to erythrose 4-phosphate and fructose 6-phosphate, while transketolase is another enzyme catalyzing the xylulose 5-phosphate and ribose 5-phosphate into sedoheptulose 7-phosphate and glyceraldehyde 3-phosphate. So, this is the key difference between transaldolase and transketolase. Besides, TALDO1 gene codes for transaldolase while TKT gene codes for transketolase.
Moreover, transaldolase transfers a three-carbon unit, while transketolase transfers a two-carbon unit. Therefore, we can consider this as another difference between transaldolase and transketolase. Furthermore, transaldolase is a pyridoxal phosphate (PLP)-dependent enzyme, while transketolase is a thiamine pyrophosphate (vitamin B1)-dependent enzyme.
Below infographic tabulates the differences between transaldolase and transketolase.
Summary – Transaldolase vs Transketolase
Transaldolase and transketolase are two enzymes involved in the non-oxidative phase of the pentose phosphate pathway. These enzymes link glycolysis and pentose phosphate pathway. Transaldolase catalyzes the transformation of sedoheptulose 7-phosphate and glyceraldehydes 3-phosphate to erythrose 4-phosphate and fructose 6-phosphate. Meanwhile, transketolase catalyzes the transformation of xylulose 5-phosphate and ribose 5-phosphate into sedoheptulose 7-phosphate and glyceraldehyde 3-phosphate. So, this is the key difference between transaldolase and transketolase.
Reference:
1. Berg, Jeremy M. “20.3 The Pentose Phosphate Pathway Generates NADPH and Synthesizes Five-Carbon Sugars.” Biochemistry. 5th Edition., U.S. National Library of Medicine, 1 Jan. 1970, Available here.
2. “Transaldolase.” Wikipedia, Wikimedia Foundation, 23 Sept. 2019, Available here.
Image Courtesy:
1. “Transaldolaseribbon” By Kurtwhite 2009 at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “E4P in Transketolase Active Site” (CC BY 3.0) via Commons Wikimedia