Table 4.
Differential Properties of Nitric Oxide Synthase Isoforms
| nNOS | iNOS | eNOS | |
|---|---|---|---|
| Type | I | II | III |
| Origin | Neurons | Macrophage | Endothelium |
| Other site of expression | VSMC | Endothelium, VSMC | VSMC, neurons |
| Expression | Constitutive | Inducible | Constitutive |
| Molecular mass (kDa) | 140 | 130 | 130 |
| mRNA size (kb) | 10 | 4.0–5.0 | 4.4 |
| Ca/CaM independent | |||
| Regulation | Ca/CaM | Transcription | Ca/CaM |
| Activation | Stimuli | Injury | Shear stress |
| Activator | Glutamate | Cytokines | Acetylcholine |
| Phosphorylation | PKA | PKA | PKA |
| N-myristoylation site | NO | No | Yes |
| NO Production | Moderate (nM to μM) | High (μM) | low (pM to nM) |
| Function | Signaling | Toxin/immune defense | Signaling |
Designations and characteristics of each NOS isoform: NOS, nitric oxide synthase; nNOS, neuronal NOS; iNOS, inducible NOS; eNOS, endothelial NOS.
PKA, protein kinase A; VSMC, vascular smooth muscle cell.