Molecular cloning and characterization of a cDNA encoding pea monodehydroascorbate reductase

Area of Science:

• Plant biochemistry
• Enzymology
• Antioxidant systems

Background:

• Monodehydroascorbate radicals are generated in plant cells through enzymatic and nonenzymatic oxidation of ascorbate.
• Ascorbate regeneration is crucial for maintaining reduced ascorbate pools, a vital antioxidant.
• Monodehydroascorbate reductase (MDHAR) plays a key role in this regeneration process.

Purpose of the Study:

• To investigate the structure, function, and regulation of monodehydroascorbate reductase.
• To achieve molecular cloning and characterization of pea (Pisum sativum L.) monodehydroascorbate reductase.

Main Methods:

• Molecular cloning of the cDNA encoding pea monodehydroascorbate reductase.
• Expression of the enzyme in Escherichia coli fused to maltose-binding protein.
• Enzymatic assays and Northern blot analysis.

Main Results:

• A cDNA encoding a 433-amino acid polypeptide for pea monodehydroascorbate reductase was cloned and characterized.
• The deduced amino acid sequence shows significant identity to soybean and cucumber MDHAR and contains NAD(P)H and FAD binding domains.
• Expressed pea MDHAR exhibited enzymatic properties similar to purified soybean and cucumber enzymes, and its transcript was found at low levels in all examined plant tissues.

Conclusions:

• The cloned pea monodehydroascorbate reductase possesses conserved functional domains and enzymatic activity.
• The enzyme's carboxyl-terminal sequence suggests potential peroxisomal targeting.
• This research provides insights into the molecular characteristics and expression of a key enzyme in plant antioxidant defense.