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Purification and characterization of monodehydroascorbate reductase from soybean root nodules.
D A Dalton1, L Langeberg, M Robbins
1Department of Biology, Reed College, Portland, Oregon 97202.
Archives of Biochemistry and Biophysics
|January 1, 1992
Summary
Soybean root nodules contain monodehydroascorbate reductase (MR), a key enzyme in the ascorbate-glutathione cycle. This study details the purification and characterization of MR, revealing its properties and role in plant defense.
Area of Science:
- Biochemistry
- Plant Physiology
- Enzymology
Background:
- Soybean root nodules possess enzymes crucial for the ascorbate-glutathione cycle, acting as a defense mechanism against reactive oxygen species.
- Monodehydroascorbate reductase (MR) is identified as a key enzyme within this cycle.
Purpose of the Study:
- To purify and characterize monodehydroascorbate reductase (MR) from soybean root nodules.
- To elucidate the enzymatic properties, isozyme forms, and kinetic parameters of MR.
Main Methods:
- Purification of MR using biochemical techniques, achieving a 646-fold increase in specific activity.
- Analysis of enzyme purity and subunit composition via SDS-PAGE.
- Characterization of kinetic properties including substrate specificity, Km values, pH optimum, and N-terminal sequencing.
Main Results:
- Purified MR appeared as a single band on SDS-PAGE, indicating high purity.
- Two isozymes (MR I and MR II) were identified with distinct molecular masses (39,000 and 40,000 Da).
- Kinetic analysis revealed specific Km values for NADH, NADPH, and monodehydroascorbate, with an optimal pH of 8-9.
Conclusions:
- The purified MR is crucial for the ascorbate-glutathione cycle in soybean root nodules, contributing to oxidative stress defense.
- The enzyme's properties suggest its specific role in the cycle, distinct from leghemoglobin reductase activity.
- Further investigation into the N-terminal sequence may reveal evolutionary relationships and functional insights.