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Macrophages can convert citrulline into arginine
1Department of Biochemistry, Memorial University of Newfoundland, St. John's, Newfoundland, Canada.
The Biochemical Journal
|January 1, 1992
Summary
Macrophages can recycle citrulline to arginine, a process crucial for sustained nitric oxide (NO) production. This citrulline-arginine cycle is enhanced by lipopolysaccharide (LPS) treatment, impacting NO generation.
Area of Science:
- Biochemistry
- Immunology
- Cell Biology
Background:
- Macrophages play a critical role in immune responses.
- Nitric oxide (NO) is a key signaling molecule produced by macrophages.
- The synthesis and regulation of arginine, a precursor to NO, are essential.
Purpose of the Study:
- To investigate the potential for citrulline recycling to arginine in rat macrophages.
- To determine the effect of lipopolysaccharide (LPS) on this citrulline-arginine pathway.
- To explore the regulatory mechanisms of arginine synthesis from citrulline.
Main Methods:
- Incubation of rat peritoneal macrophages with radiolabeled [14C]citrulline.
- Measurement of [14C]arginine synthesis rates.
- Quantification of nitrate production as an indicator of NO generation.
- Assessment of the effects of L-glutamine and L-arginine on citrulline-arginine synthesis.
Main Results:
- Macrophages synthesized arginine from citrulline, with rates sensitive to extracellular citrulline concentrations.
- LPS treatment significantly increased both arginine synthesis from citrulline and NO production.
- L-glutamine partially inhibited arginine synthesis, while L-arginine inhibited it only in control cells.
Conclusions:
- Rat macrophages possess a functional citrulline-arginine recycling pathway.
- This pathway is upregulated by LPS and contributes to arginine availability for NO synthesis.
- The citrulline-arginine cycle is a significant factor in regulating sustained NO production by macrophages.