Reductases for carbonyl compounds in human liver

Area of Science:

• Biochemistry
• Enzymology
• Human Physiology

Background:

• Human liver cytosol contains enzymes crucial for metabolizing aldehydes and ketones.
• Understanding the specific roles and properties of these reductases is vital for comprehending metabolic pathways.

Purpose of the Study:

• To purify and characterize aldehyde and carbonyl reductases from human liver cytosol.
• To compare the enzymatic properties and substrate specificities of these reductases with alcohol dehydrogenase.

Main Methods:

• Purification of enzymes to homogeneity from human liver cytosol.
• Characterization of enzyme properties including molecular weight, pI, cofactor preference, pH optima, and substrate specificity.
• Enzyme activity assays and kinetic analysis.
• Starch gel electrophoresis for enzyme identification.

Main Results:

• Three reductases were purified: a high molecular weight aldehyde reductase (identified as alcohol dehydrogenase), a lower molecular weight aldehyde reductase, and a carbonyl reductase.
• Alcohol dehydrogenase exhibited preference for NADH, reduced various aldehydes and ketones, and showed optimal activity at pH 6.0 (reduction) and 8.8 (oxidation).
• The other two reductases were NADPH-dependent with distinct substrate specificities and sensitivities to inhibitors. Alcohol dehydrogenase displayed the highest affinity and kcat for aldehydes.

Conclusions:

• Human liver cytosol possesses multiple reductase enzymes with overlapping and distinct functions.
• Alcohol dehydrogenase is a highly efficient enzyme for aldehyde reduction in the liver.
• Characterization of these reductases provides insights into their physiological roles and potential involvement in drug metabolism.