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On the substrate specificity of nitric oxide synthase
M Hecker1, D T Walsh, J R Vane
1William Harvey Research Institute, St. Bartholomew's Hospital Medical College, London, UK.
FEBS Letters
|December 9, 1991
Summary
Researchers identified at least three nitric oxide (NO) synthase (NOS) isoforms. These isoforms differ in their cellular location, calcium dependency, and substrate specificity, impacting NO production.
Area of Science:
- Biochemistry
- Cell Biology
- Physiology
Background:
- Nitric oxide (NO) synthase (NOS) plays a crucial role in cellular signaling.
- Understanding NOS isoforms and their regulation is key to comprehending NO's diverse functions.
Purpose of the Study:
- To investigate the activity and characteristics of NOS in different cellular fractions.
- To differentiate between constitutive NOS (NOSc) and inducible NOS (NOSi) based on location and dependency.
Main Methods:
- Assayed NOS activity by measuring NO-mediated cyclic GMP increase in LLC-PK1 cells.
- Examined NOS activity in subcellular fractions (cytosol and membrane) of endothelial cells (EC) and J774.2 macrophages.
- Investigated substrate specificity using L-Homoarginine and L-arginine peptides.
Main Results:
- Constitutive NOS in EC was primarily membrane-bound, while inducible NOS in J774.2 cells was cytosolic and membrane-associated.
- Ca(2+)-dependency varied: cytosolic NOSc (EC) and membrane NOSi (J774.2) were Ca(2+)-dependent; membrane NOSc (EC) and cytosolic NOSi (J774.2) were Ca(2+)-independent.
- L-Homoarginine and specific peptides substituted L-arginine for NOSc (EC) and Ca(2+)-independent NOSi (J774.2), but not for Ca(2+)-dependent NOSi.
Conclusions:
- At least three distinct NOS isoforms exist, distinguishable by their intracellular localization, Ca(2+)-dependency, and substrate preferences.
- These findings highlight the complexity of NOS regulation and function in different cell types.