Low apparent aldose reductase activity produced by monosaccharide autoxidation

Area of Science:

• Biochemistry
• Enzymology
• Chemical Kinetics

Background:

• Aldose reductase activity is often measured by NADPH oxidation.
• Apparent low aldose reductase activity can be influenced by experimental conditions.
• Monosaccharide autoxidation is a known chemical process.

Purpose of the Study:

• To investigate the role of monosaccharide autoxidation in apparent aldose reductase activity.
• To determine if sugar autoxidation can lead to NADPH oxidation.
• To explain non-linear kinetics observed in aldose reductase assays.

Main Methods:

• Measuring NADPH oxidation rates in solutions of autoxidizing DL-glyceraldehyde.
• Analyzing the effects of buffer conditions, monosaccharide structure, and temperature.
• Investigating the influence of nucleotide-binding proteins and glutathione reductase.
• Testing the effects of aldose reductase inhibitors on NADPH oxidation.

Main Results:

• Autoxidizing DL-glyceraldehyde oxidized NADPH at significant rates.
• Monosaccharide autoxidation was a prerequisite for NADPH oxidation, likely via a hydroperoxy radical.
• Nucleotide-binding proteins, like glucose-6-phosphate dehydrogenase, enhanced NADPH oxidation.
• Aldose reductase inhibitors acted as antioxidants, inhibiting NADPH oxidation.

Conclusions:

• Low apparent aldose reductase activity may result from monosaccharide autoxidation artifacts.
• Sugar autoxidation provides a potential explanation for non-linear steady-state kinetics observed with DL-glyceraldehyde and aldose reductase.
• Careful consideration of monosaccharide stability is crucial in aldose reductase research.