NOX-like ROS production by glutathione reductase

Area of Science:

• Biochemistry
• Marine Biology
• Cellular Biology

Background:

• NADPH oxidase (NOX) enzymes produce reactive oxygen species (ROS) like superoxide (O₂^-) in many organisms.
• Previous research identified glutathione reductase (GR) as a potential extracellular superoxide source in the marine diatom *Thalassiosira oceanica*.

Purpose of the Study:

• To express and characterize the two GR isoforms from *T. oceanica*.
• To investigate the mechanism and physiological role of GR-mediated superoxide production.

Main Methods:

• Expression and biochemical characterization of *T. oceanica* GR isoforms.
• Enzyme kinetics assays measuring NADPH oxidation and superoxide production.
• Inhibition assays to assess enzyme activity and specificity.

Main Results:

• Both *T. oceanica* GR isoforms produced superoxide by coupling NADPH oxidation to oxygen reduction, independent of their native electron acceptor, glutathione disulfide.
• Superoxide production by ToGR1 showed kinetics comparable to NOX enzymes.
• Inhibition assays supported a physiological role for GR in superoxide production, consistent with prior organismal studies.

Conclusions:

• *Thalassiosira oceanica* GR isoforms can function as superoxide-producing enzymes, similar to NOX.
• GR-mediated ROS production is independent of iron, offering a potential advantage under micronutrient stress.
• The similarity of ToGR to GR from other species suggests this NOX-like ROS production mechanism may be widespread across diverse organisms.