Inactivation of human aldehyde dehydrogenase by isosorbide dinitrate

Area of Science:

• Biochemistry
• Enzymology

Background:

• Human aldehyde dehydrogenase (EC 1.2.1.3) exists as E1 and E2 isozymes.
• Isosorbide dinitrate is a nitrate ester drug.

Purpose of the Study:

• To investigate the mechanism by which isosorbide dinitrate inactivates human aldehyde dehydrogenase.
• To characterize the products and kinetics of this inactivation process.

Main Methods:

• Enzyme kinetics studies using purified human aldehyde dehydrogenase isozymes.
• Incubation with isosorbide dinitrate at varying temperatures (0°C and 25°C).
• Analysis of reaction products and enzyme activity using radiolabeled compounds and inhibitors.

Main Results:

• Isosorbide dinitrate irreversibly inactivated both E1 and E2 isozymes, abolishing dehydrogenase and esterase activities.
• Inactivation was associated with the formation of isosorbide-2-mononitrate and isosorbide-5-mononitrate.
• A mechanism-based inactivation involving enzyme sulfhydryls and the esterase function was proposed, with isosorbide-2-mononitrate identified as a potent inactivator.

Conclusions:

• Isosorbide dinitrate acts as a mechanism-based inactivator of human aldehyde dehydrogenase.
• The esterase activity of the enzyme is crucial for this inactivation process.
• The formation of mononitrate products and potential sulfhydryl modification are key features of the inactivation pathway.