A highly specific L-galactose-1-phosphate phosphatase on the path to ascorbate biosynthesis

Area of Science:

• Biochemistry
• Plant Physiology
• Enzymology

Background:

• Ascorbate (vitamin C) is essential for plants and animals, with humans relying on plants for dietary intake.
• The precise biochemical pathway for ascorbate synthesis in plants remains incompletely understood, with several enzymes yet to be identified.

Purpose of the Study:

• To identify and characterize a specific enzyme involved in the plant ascorbate biosynthesis pathway.
• To elucidate the role of L-galactose-1-phosphate phosphatase in vitamin C production in plants.

Main Methods:

• Partial purification and biochemical characterization of L-galactose-1-phosphate phosphatase from kiwifruit (Actinidia deliciosa) berries.
• Comparative analysis of the enzyme's properties with a similar enzyme from Arabidopsis thaliana.
• Protein identification using liquid chromatography-mass spectrometry (LC-MS) after trypsin digestion.
• Gene cloning and expression of a kiwifruit ascorbate pathway enzyme homologue in Escherichia coli.

Main Results:

• A kiwifruit enzyme, L-galactose-1-phosphate phosphatase, was purified and characterized, showing specific activity towards L-galactose-1-phosphate and dependence on Mg2+.
• The enzyme exhibited optimal activity at pH 7.0 with specific kinetic parameters (K M and K a).
• An analogous enzyme from Arabidopsis thaliana shared similar properties. LC-MS identified a putative myo-inositol-1-phosphate phosphatase (At3g02870) as the likely L-galactose-1-phosphate phosphatase.
• An expressed kiwifruit homologue demonstrated significantly higher activity for L-galactose-1-phosphate compared to myo-inositol-1-phosphate, confirming its role.

Conclusions:

• The identified L-galactose-1-phosphate phosphatase is a key enzyme in the ascorbate biosynthesis pathway in plants.
• This finding contributes significantly to understanding how plants produce vitamin C, a crucial nutrient for human health.
• The study provides a molecular basis for further research into ascorbate production and regulation in plants.