Conversion of a NADPH-dependent aldehyde reducing enzyme into aldose reductase

Area of Science:

• Biochemistry
• Enzymology
• Nephrology

Background:

• Aldose reductase and aldehyde reductase play roles in polyol metabolism.
• Understanding different reductase isoforms in kidney medulla is crucial for metabolic studies.

Purpose of the Study:

• To purify and characterize aldose reductase, aldehyde reductase, and high-Km aldose reductase from dog kidney inner medulla.
• To compare the biochemical and immunochemical properties of these enzymes.
• To investigate the relationship between high-Km aldose reductase and aldose reductase.

Main Methods:

• Purification of enzymes from dog kidney inner medulla.
• Enzyme activity assays for aldo-sugars.
• Isoelectric focusing and molecular weight determination.
• Inhibition studies using aldose reductase inhibitors.
• Immunochemical analysis.
• Incubation studies to assess enzyme conversion.

Main Results:

• High-Km aldose reductase exhibited distinct properties from aldose reductase, including lower isoelectric point, reduced aldo-sugar activity, and lower inhibitor sensitivity.
• Both high-Km aldose reductase and aldose reductase shared the same molecular weight and immunochemical characteristics.
• High-Km aldose reductase was readily converted into an aldose reductase-like 'generated reductase' in neutral buffer.
• The generated reductase was biochemically and immunochemically identical to aldose reductase.

Conclusions:

• Dog kidney inner medulla contains distinct aldose reductase and high-Km aldose reductase isoforms.
• High-Km aldose reductase can be converted into an aldose reductase-like enzyme, suggesting a precursor-product relationship or conformational change.
• These findings contribute to understanding the enzymatic machinery involved in polyol metabolism within the kidney.