From the Guidelines
The substrate for nitric oxide synthetase is L-arginine, which corresponds to option (c). Nitric oxide synthetase (NOS) is an enzyme that catalyzes the production of nitric oxide (NO) from L-arginine. During this reaction, L-arginine is converted to L-citrulline while producing nitric oxide as a byproduct. This process requires oxygen and NADPH as co-substrates, along with several cofactors including tetrahydrobiopterin (BH4), FAD, FMN, and heme. Nitric oxide is an important signaling molecule in the body with various physiological functions including vasodilation, neurotransmission, and immune defense. There are three main isoforms of NOS: neuronal NOS (nNOS), inducible NOS (iNOS), and endothelial NOS (eNOS), all of which use L-arginine as their primary substrate, as indicated by 1.
Some key points to consider:
- L-arginine is the sole substrate for NOS and thus is essential for NO production, as stated in 1.
- The other amino acids listed - glutamine, alanine, and valine - are not substrates for this enzyme.
- The most recent and highest quality study, 1, also confirms that L-arginine is the substrate for nitric oxide synthetase.
- The reaction catalyzed by NOS requires several cofactors, including tetrahydrobiopterin (BH4), FAD, FMN, and heme, as mentioned in 1.
- Nitric oxide has various physiological functions, including vasodilation, neurotransmission, and immune defense, as discussed in 1.
Overall, the evidence from the studies 1 supports the conclusion that L-arginine is the substrate for nitric oxide synthetase.
From the Research
Substrate for Nitric Oxide Synthetase
The substrate for nitric oxide synthetase is:
Key Points
- L-arginine is the precursor for the synthesis of nitric oxide (NO) via NO synthase (NOS) 2, 3, 4
- L-arginine transport mechanisms play a major role in the regulation of NO-dependent function 3, 6
- Endogenous NO formation is dependent on extracellular L-arginine concentrations 3
- L-arginine deficiency syndromes in humans involve endothelial inflammation and immune dysfunctions 2
- L-arginine supplementation may be a novel therapy for obesity and metabolic syndrome 2