Transaldolase

Transaldolase

Ribbon diagram of transaldolase

Transaldolase is an enzyme that plays a crucial role in the pentose phosphate pathway, a metabolic pathway parallel to glycolysis. It is involved in the reversible transfer of a three-carbon dihydroxyacetone moiety from a ketose donor to an aldose acceptor.

Function

Transaldolase catalyzes the reaction:

Sedoheptulose 7-phosphate + Glyceraldehyde 3-phosphate _ Erythrose 4-phosphate + Fructose 6-phosphate

This reaction is part of the non-oxidative phase of the pentose phosphate pathway, which is important for the generation of NADPH and the synthesis of ribose 5-phosphate, a precursor for nucleotide synthesis.

Mechanism

Mechanism of transaldolase action

The mechanism of transaldolase involves the formation of a Schiff base intermediate between the enzyme and the substrate. The active site of transaldolase contains a lysine residue that forms a covalent bond with the substrate, facilitating the transfer of the three-carbon unit.

Structure

Active site of transaldolase

Transaldolase is a protein that typically forms a homodimer or homotetramer. The structure of transaldolase has been elucidated through X-ray crystallography, revealing the arrangement of its active site and the residues involved in catalysis.

Biological Significance

The pentose phosphate pathway, in which transaldolase participates, is essential for cellular metabolism. It provides reducing power in the form of NADPH, which is necessary for biosynthetic reactions and for maintaining the redox balance in cells. Additionally, the pathway supplies ribose 5-phosphate for nucleotide and nucleic acid synthesis.

Clinical Relevance

Deficiencies in transaldolase activity can lead to metabolic disorders. For example, transaldolase deficiency is a rare genetic condition that can result in liver dysfunction, growth retardation, and other systemic issues due to the accumulation of sugar phosphates and the disruption of normal metabolic processes.

Related Pages

• Pentose phosphate pathway
• Glycolysis
• NADPH
• Ribose 5-phosphate

References

• 
  Transaldolase
• 
  Transaldolase Active Site
• 
  Transaldolase Mechanism
• Transaldolase in Pentose Phosphate Pathway
  Transaldolase in Pentose Phosphate Pathway