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Nitric oxide inhibits ornithine decarboxylase by S-nitrosylation
P M Bauer1, J M Fukuto, G M Buga
1Department of Molecular and Medical Pharmacology, University of California-Los Angeles School of Medicine, Los Angeles, California, 90095-1735, USA.
Abstract:
Ornithine decarboxylase (ODC) is the initial enzyme in the polyamine synthetic pathway, and polyamines are required for cell proliferation. We have shown previously that nitric oxide (NO) inhibits ODC activity in Caco-2 cells and in crude cell lysate preparations. In this study we examined the mechanism by which NO inhibits the activity of purified ODC. NO, in the form of S-nitrosocysteine (CysNO), S-nitrosoglutathione (GSNO), or 1, 1-diethyl-2-hydroxy-2-nitroso-hydrazine (DEA/NO), inhibited enzyme activity in a concentration-dependent manner. CysNO (1 microM) inhibited ODC activity by approximately 90% and 3 microM GSNO by more than 70%. DEA/NO was less potent, inhibiting enzyme activity by 70% at a concentration of 30 microM. Inhibition of enzyme activity by CysNO, GSNO, or DEA/NO was reversible by addition of dithiothreitol or glutathione. Cuprous ion (Cu (I)) also reversed the inhibitory effect of these NO donor agents. The data presented here support the hypothesis that NO inhibits ODC activity via S-nitrosylation of a critical cysteine residue(s) on ODC.
Insights
Nitric oxide (NO) inhibits ornithine decarboxylase (ODC) activity by S-nitrosylation. This reversible inhibition affects polyamine synthesis, crucial for cell proliferation.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Ornithine decarboxylase (ODC) is key in polyamine synthesis, essential for cell proliferation.
- Nitric oxide (NO) has been previously shown to inhibit ODC activity.
Purpose of the Study:
- To investigate the mechanism by which nitric oxide (NO) inhibits purified ornithine decarboxylase (ODC) activity.
Main Methods:
- Used various NO donors (S-nitrosocysteine, S-nitrosoglutathione, DEA/NO) to treat purified ODC.
- Assessed enzyme activity inhibition in a concentration-dependent manner.
- Investigated reversibility of inhibition using dithiothreitol, glutathione, and cuprous ion.
Main Results:
- NO donors inhibited ODC activity in a concentration-dependent manner.
- Inhibition was reversible by reducing agents and cuprous ion.
- S-nitrosocysteine and S-nitrosoglutathione were potent inhibitors.
Conclusions:
- Nitric oxide (NO) inhibits ornithine decarboxylase (ODC) activity through S-nitrosylation of critical cysteine residues.
- This mechanism impacts polyamine synthesis and cell proliferation.