**Core Concept**
Nitric oxide (NO) is a potent vasodilator that plays a crucial role in vascular tone regulation. It is synthesized from the amino acid L-arginine in the endothelium through a process involving the enzyme nitric oxide synthase (NOS).

**Why the Correct Answer is Right**
Nitric oxide is indeed derived from L-arginine, which is converted into citrulline by the action of NOS. This enzyme catalyzes the transfer of a nitrogen atom from L-arginine to molecular oxygen, resulting in the production of nitric oxide. The reaction is as follows: L-arginine + NADPH + O2 → citrulline + nitric oxide (NO). Nitric oxide then diffuses into the smooth muscle cells of the blood vessel wall, causing relaxation and vasodilation.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not relevant to the derivation of nitric oxide.
**Option B:** This option is incorrect as nitric oxide is not derived from tyrosine.
**Option C:** This option is incorrect as nitric oxide is not derived from tryptophan.

**Clinical Pearl / High-Yield Fact**
The endothelium-dependent relaxation of blood vessels is a critical mechanism for maintaining normal blood pressure and flow. This process is often impaired in conditions such as atherosclerosis and hypertension.

**Correct Answer:** C.