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Catalase-peroxidases (KatG) exhibit NADH oxidase activity
Rahul Singh1, Ben Wiseman, Taweewat Deemagarn
1Department of Microbiology, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada.
The Journal of Biological Chemistry
|July 29, 2004
Summary
Catalase-peroxidases (KatG) from bacteria like Mycobacterium tuberculosis can activate isoniazid (INH) into its toxic form, isonicotinoyl-NAD, by oxidizing NADH. This discovery offers new insights into drug activation mechanisms.
Area of Science:
- Biochemistry
- Microbiology
- Enzymology
Background:
- Catalase-peroxidases (KatG) are enzymes found in various bacteria, including pathogens like Mycobacterium tuberculosis.
- These enzymes possess multiple catalytic activities, including peroxidase and catalase functions.
Purpose of the Study:
- To investigate the NADH oxidase activity of bacterial KatG enzymes.
- To explore the potential of KatG in catalyzing isoniazid (INH) activation.
- To elucidate the mechanism of isonicotinoyl-NAD formation.
Main Methods:
- Enzyme kinetics studies to determine kinetic parameters (Km, kcat) for NADH oxidation.
- pH profiling to differentiate enzymatic activities.
- High-performance liquid chromatography (HPLC) and mass spectrometry for product identification.
- Investigating the effect of manganese ions on the reaction.
Main Results:
- Bacterial KatG enzymes exhibit NADH oxidase activity with a pH optimum of 8.75, distinct from their peroxidase and catalase activities.
- KatG catalyzes the oxygen- and H2O2-independent hydrazinolysis of isoniazid (INH).
- A coupled reaction of NADH and INH yields isonicotinoyl-NAD, the active form of isoniazid, with increased efficiency in M. tuberculosis KatG.
- Manganese ions activate the synthesis of isonicotinoyl-NAD.
Conclusions:
- Bacterial catalase-peroxidases play a significant role in the activation of isoniazid.
- The NADH oxidase activity of KatG is crucial for generating the activated drug form.
- This mechanism is particularly relevant for the efficacy of isoniazid against Mycobacterium tuberculosis.