Molecular characterization of Euglena ascorbate peroxidase using monoclonal antibody

Area of Science:

• Biochemistry
• Enzymology
• Plant Science

Background:

• Ascorbate peroxidase (APX) is crucial for antioxidant defense in plants.
• Understanding APX diversity across different organisms, like Euglena gracilis, is important.
• Cytosolic and chloroplastic APX isozymes are well-studied in higher plants.

Purpose of the Study:

• To purify and characterize ascorbate peroxidase from Euglena gracilis Z.
• To compare its properties with APX enzymes from higher plants.
• To investigate its evolutionary relationship with other APX enzymes.

Main Methods:

• Purification of ascorbate peroxidase to electrophoretic homogeneity.
• Determination of molecular mass using SDS-PAGE and gel filtration.
• Analysis of substrate specificity and enzyme stability.
• N-terminal amino-acid sequencing and peptide analysis.
• Preparation and characterization of monoclonal antibodies (EAP1, EAP2) via Western blot analysis.

Main Results:

• Purified Euglena APX is a monomeric enzyme (58 kDa).
• It reduces both hydrogen peroxide and organic hydroperoxides, similar to higher plant cytosolic isozymes.
• N-terminal sequence shows low similarity to higher plant APX, but peptide sequences exhibit high homology.
• Monoclonal antibodies EAP1 and EAP2 show homology to higher plant cytosolic APX; EAP1 cross-reacts with spinach chloroplastic APX.

Conclusions:

• Euglena gracilis ascorbate peroxidase possesses characteristics of both cytosolic and chloroplastic APX from higher plants.
• Despite sequence differences, conserved homologous regions suggest evolutionary links.
• The enzyme's properties and antibody cross-reactivity highlight conserved features of APX across diverse eukaryotes.