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Monitoring the Reductive and Oxidative Half-Reactions of a Flavin-Dependent Monooxygenase using Stopped-Flow Spectrophotometry
Published on: March 18, 2012
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Riboflavin compounds show NAD(P)H dependent quinone oxidoreductase-like quinone reducing activity
Midori Nagase1, Miku Sakamoto1, Sakiko Amekura1
1School of Bioscience and Biotechnology, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.
Journal of Clinical Biochemistry and Nutrition
|August 3, 2023
Summary
Researchers discovered that riboflavin, not NQO1, reduces coenzyme Q10 in rat liver. This flavin-dependent pathway may be crucial for antioxidant defense in cellular fluids.
Area of Science:
- Biochemistry
- Cell Biology
- Oxidative Stress Research
Background:
- NAD(P)H-dependent quinone oxidoreductase (NQO) is vital for cellular protection against oxidative stress.
- NQO enzymes facilitate the reduction of coenzyme Q (CoQ) using NAD(P)H as an electron donor.
Purpose of the Study:
- To investigate the source of coenzyme Q10 reducing activity in rat liver homogenate.
- To differentiate the activity from known NQO enzymes and identify the responsible compound.
Main Methods:
- Gel filtration chromatography of rat liver homogenate.
- Enzyme inhibition assays using dicumarol and quercetin.
- Purification and identification of the active compound.
- Testing the reducing activity of identified compounds on CoQ and vitamin K homologues.
Main Results:
- Coenzyme Q10 reducing activity was found in both high-molecular-weight (NQO) and low-molecular-weight fractions.
- The low-molecular-weight activity was not inhibited by dicumarol but was inhibited by quercetin.
- NADH-dependent CoQ10 reduction was identified as being mediated by riboflavin.
- Riboflavin, FAD, and FMN, in conjunction with NADH, reduced CoQ and vitamin K homologues.
Conclusions:
- Riboflavin, not NQO1, is responsible for a significant portion of NADH-dependent CoQ10 reduction in rat liver.
- This flavin-dependent reduction mechanism, potentially involving saposin B, may operate in aqueous cellular compartments.
- The findings suggest a novel pathway for antioxidant defense and CoQ reduction in biological systems.
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