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Isolation and characterization of a mitochondrial D-amino acid oxidase from Neurospora crassa
Abstract:
D-Amino acid oxidase (EC 1.4.3.3) activity in homogenates of Neurospora crassa strain SY7A was found to sediment with the mitochondrial fraction. Digitonin fractionation studies on purified mitochondria have indicated a matrix localization of the enzyme. Additionally, a peroxidase (EC 1.11.1.7) activity, which may remove hydrogen peroxide formed as a product of D-amino acid oxidation, was also found in the mitochondrial matrix. Partial purification (20- to 30-fold) of the mitochondrial D-amino acid oxidase was achieved. The enzyme exhibited a pH optimum between 9.0 and 9.2, temperature optimum between 20 and 30 degrees C, and a molecular weight of 118 000 +/- 6000 as determined by gel electrophoresis and 125 000 as determined by gel chromatography.
Insights
D-Amino acid oxidase activity in Neurospora crassa is located in the mitochondrial matrix. This enzyme, along with a peroxidase, plays a role in managing oxidative byproducts during D-amino acid metabolism.
Area of Science:
- Biochemistry
- Molecular Biology
- Mycology
Background:
- D-Amino acid oxidase (EC 1.4.3.3) is an enzyme involved in amino acid metabolism.
- Understanding the localization and properties of D-amino acid oxidase in eukaryotic organisms like Neurospora crassa is crucial for elucidating its biological functions.
- Hydrogen peroxide, a byproduct of D-amino acid oxidation, necessitates detoxification mechanisms within the cell.
Purpose of the Study:
- To determine the subcellular localization of D-amino acid oxidase activity in Neurospora crassa.
- To investigate the presence and localization of a peroxidase activity that may handle hydrogen peroxide generated by D-amino acid oxidase.
- To achieve partial purification of the mitochondrial D-amino acid oxidase and characterize its basic properties.
Main Methods:
- Differential centrifugation of Neurospora crassa homogenates to isolate mitochondrial fractions.
- Digitonin fractionation of purified mitochondria to pinpoint enzyme localization within mitochondrial compartments.
- Enzyme assays to detect D-amino acid oxidase and peroxidase activities.
- Partial enzyme purification techniques.
- Biophysical methods (gel electrophoresis, gel chromatography) to determine molecular weight and characterize enzyme properties.
Main Results:
- D-Amino acid oxidase activity was predominantly found in the mitochondrial fraction of Neurospora crassa.
- Further fractionation studies localized the enzyme to the mitochondrial matrix.
- A peroxidase activity, potentially involved in hydrogen peroxide removal, was also identified in the mitochondrial matrix.
- Partial purification (20-30 fold) of the mitochondrial D-amino acid oxidase was successful.
- The purified enzyme exhibited a pH optimum of 9.0-9.2 and a temperature optimum of 20-30°C.
- Molecular weight was estimated to be approximately 118,000-125,000 Da.
Conclusions:
- D-Amino acid oxidase in Neurospora crassa is a mitochondrial matrix enzyme.
- The co-localization with peroxidase suggests a coordinated role in managing oxidative stress from D-amino acid metabolism.
- The characterized properties provide a foundation for further biochemical and genetic studies of this enzyme in fungi.