Table 1.

Characteristics of NOS Isoforms

Isoform	nNOS	iNOS	eNOS
Other names	NOS-1, NOSI, Type I NOS	NOS-2, NOSII, Type II NOS	NOS-3, NOSIII, Type III NOS
Human chromosomal location	12q24.2-12q24.3	17cen-q11.2	7q35–7q36
Human gene structure and size	29 exons	26 exons	26 exons
	locus region >200 kbp	37 kbp	21–22 kbp
Human monomer size (predominant form)	161 kDa	131 kDa	133 kDa
Splice variants	Yes	Yes	No
Typical site of expression	Neurons	Macrophages	Endothelial cells
Other major sites of expression	Smooth muscle	Smooth muscle	Smooth muscle
	Skeletal muscle	Liver	Platelets
Gene expression	Constitutive and inducible	Inducible	Constitutive and inducible
Ca²⁺ dependency	Ca²⁺-dependent	Practically Ca²⁺-independent	Ca²⁺-dependent
Covalent modifications	Phosphorylation		Myristoylation
			Palmitoylation
			Phosphorylation
Protein–protein interactions	hsp90, caveolin, NOSIP		hsp90, caveolin
Subcellular localization	Neuromuscular junction	Soluble	Caveolae
	Soluble
	Sarcoplasmic reticulum
Means of localization	N-terminal PDZ domain (for membrane association)	N/A	N-terminal myristoylation
NO production (range)	Moderate (nM to μM)	High (μM)	Low (pm to nM)